Nice tall mountains! I presume the computer inside is for programming the decoders?
I've got my track issues (outside the yard, which I really haven't dived into yet) resolved, except for 3 things:
1) The monster still only runs on one loop. I can make it run on the other loop if I smooth out the track between the wye turnout at the siding and the bridge right before the #2 turnout, which is really ok, just too abrupt a change in grade for the length of the monster. Getting it to go over Block #7 and #8 is not going to happen. When coming out of the #1 turnout, the rise coming into it from the yard followed by the fall afterwards as it goes into the turn around the back of the layout (block #7) is just too much to overcome, and I already messed with it enough to get the NYC diesel over that area. Coming out of the tunnel in block #8 to cross the bridge might be doable, and may end up needing work anyhow for the other locomotives, but there's no point in getting the monster to do it if it can't get through block #7. I'm ok with that though; the fact that the monster runs on this layout at all is a miracle, and it now does the loop through the yard with no issues.
2) The bridge needs to have a careful eye kept on it. It is not secured down yet because of all the work on track, so running trains over it can cause it to start creeping. I'm leery of securing it down in case I run into other issues. Still, trains can run on it for loop after loop before it creeps to the point of a derailment.
3) Where the double bridge meets the tunnel, on the yard loop side, there is a small but visible kink in the track. Amazingly, everything seems to negotiate this kink just fine. It is a little worrisome though, and doesn't look very good. The kink results from accumulating errors in the track plan. The double bridge was the last thing installed. When I put it in, it didn't fit exactly, and getting the pilings in place around the river and the tracks beneath has been a major chore. They fit now, but previously, there was 5" of track in 2x 2 1/2" sections on the end by the grade crossing, and another 5" in a 2 1/2, 1, and 1 1/2" section at the tunnel end; I did not have enough 2 1/2" to eliminate both of the smaller pieces on the tunnel end.
Anyhow, in the process of working on getting the monster and the NYC diesel to go around the yard loop reliably, that bridge exit-tunnel entrance spot was trouble because it was practically impossible to get those 3 little pieces of track to lay flat; they hung out into space because the gap is longer than the 4x 9" bridge sections that make the double bridge. I eventually shortened the grade crossing side an inch, and replaced those 3 small pieces with a single 6" straight section. That's when the kink appeared. I suspect it was always there; it just wasn't easily seen because the kink was spread across 3 joints rather than just one. I made the kink a bit smaller by inserting a 3/4" section back farther in the curve to bring it more in line with the bridge, but it's still there. Thankfully, it doesn't seem to cause any derailments, even running at 75% on the throttle.
The new cars I got for Christmas turned out to be invaluable in finally getting the track issues worked out. I needed a train of reasonable length with high-quality, consistent performance so I could tell what problems were track and what were rolling stock. With the NYC diesel, the boxcar and caboose from my mom, and the 5 new cars I got, I was able to do that. A major lesson learned there; when diagnosing track problems, do it with new stuff, or at least stuff you know performs consistently. Also, 3 of the new cars have larger-diameter wheels, which helped me find a few other things. The NYC diesel was also invaluable; it's small enough that it reflects the other engines and doesn't have the monster's idiosyncracies, but sensitive enough to poor track to find the problems.
I do plan to cut and insert some sections of pier girder at the double bridge on the tunnel end to clean things up. Another trick I discovered was to use a 5" section of metal bracket I had; this slipped under the track at the tunnel entrance on the other track and makes it nice and stiff; the pier there previously wasn't doing it.
Here is the monster pulling an extra-long test train. I added my 5 tank cars to the new cars to see how a longer train would do; including the caboose that makes 12 cars. You can't see most of the train, but what you can see is that the front of the monster is poking out of the tunnel, while the caboose is poking out of the other end. This long train successfully made 10 trips around the yard loop with no derailments. (2 pictures) (Note: the monster was actually not running at the time of the picture; I had to stop it to get the shot.)
Below was an interesting spot. I had no problems here, until a few runs with the monster after the above changes to the pieces leading into the double bridge. You probably can't tell from this picture, but the section of track directly behind the crossing was not level; the rail closer to the camera was just slightly lower than the farther rail. This was causing the front truck on the monster's tender to derail; the wheel flange would just barely slide over the rail.
In this picture you see the fix. A very thin piece of cardboard under only that rail brings it up so the wheel flange doesn't slip over it.
That's one thing I have discovered so far: You really won't be able to tell what will cause a derailment until you test it, and look closely at exactly where the derailment occurs. If I didn't have the monster, I would have never noticed that since it only bothered that unit.
Another lesson learned: next time, I'll use foam and/or roadbed like Jerry did. Although I can scenic over these little shims I have all over the place I probably would need a lot fewer if the track was on something to smooth things out.
Going to be getting back to the mountain next. I plan to experiment with using drywall mud instead of plaster for the back half and see what comes out better.