2001 Chevy Suburban shifts fine when cold, but.

If the trans has not given you a problem before then it could be that it just needs to be flushed and the filter changed

With 141,000 on the transmission and 40,000 since the fluid and filter was changed. It is possible unless when you had the filter and fluid changed they flushed the system. Most places will drain the transmission and put a new filter on. There is a difference of flushing the system and just changing the fluid. Sometimes there is still stuff I would call it left inside the transmission itself. You said you were on your way to the gmc dealer. What was his recomendations? There could be other problems but flushing the system is the cheapest and easiest to be done. I had my system flushed on my car at a monroe muffler shop.

These days it helps to be able to save some money. I have looked around some and found that summit has a rebuilt th350 transmission for 649.95 and shipping is free, not saying that is the one you need but check around maybe you can find something that won't cost a arm or leg. There are ones on e-bay that are rebuilt for about the same price. It's up to you what you want to do.

Excuse the intrusion but I can't help jumping in because the conversation is good.I had the same problem, when my truck was cold the transmission worked perfectly and when it warmed up it would come out of gear, then I noticed my speedometer was not working, right a intermittent problem, and every time I had transmission problems the speedometer quit working, then I realized the computer controls the shifting of the transmission through the speedometer, and if the speedometer fails to work so will the transmission, it's called the speed sensor on the transmission, how is your speedometer working?

Dr loot, has a good point, how about trying to reset your computer. Has the truck been scanned for transmission errors? Try disconnecting the battery and leaving it off for a couple of minutes, then reconnect it. Most vehicles has tob be driven appox 50 miles before resetting. Ity's something to try before spending $2100.00 for a transmission.