Engine gets starts slow then speeds up

I'm trying to figure out why my engine seems to take a while to warm up. When I first bring it out, it runs very slowly and then after several runs, it eventually seems to go faster.

I just recently installed my track. It is 75' and a mix of lgb and aristo brass. I've been cleaning the track with a pole sander and making sure the pickups are clean and shiny. I've tested the voltage on the entire system and it is consistent.

I do have a 2-3% grade in some spots and the engine is so slow when it starts that it just can't make it up these hills. Once it has "perked" up it has no problem with these grades.

Jim