My 2002 envoy stalls and wont ssstart after the engineabout a mile or two drdriiving any ideas

Were you low on gas?

Sorry to say but your mechanic is probally right because 204000 miles is alot of miles for a transmission and when the clutches start to slip thats what it sounds like.

It will tend to stall when you have the A/C on and or the defrost, not the heater correct? The defrost uses the A/C to dry the air. The battery was probably disconnected or changed recently. Clean your throttle body with throttle body cleaner while the battery is disconnected. When finished, drive around for 5 miles or so with the A/C and Defroster off. Your computer will relearn the the newly cleaned throttle body. This will fix this very common problem. Will cost you about 7 bucks for the cleaner and you're gas mileage will be better.

By chance, was the battery recently unhooked? If so, clean your throttle body with the battery unhooked. Clean with carb cleaner that is approved for throttle bodies, or throttle body cleaner. Drive around for 5 or so miles after your finished, this will reset the computer. If the battery was unhooked...the symptoms would be nearly stalling, with the A/C on OR the defroster on.

At least 200K if well maintained.

Very common problem with Envoys and Trailblazers. For Driver 1 Clean your throttle body with throttle body cleaner while the battery is disconnected. After this is done, re-connect your battery, drive around for 5-10 miles while the computer resets and relearns. Do the driving with the A/C off and the defroster off. Your problem will be solved. I've never heard of not starting in a different driver mode with just changing the battery.

check your vaucumn hoses for leaks any leak in that system will effect your fuel pressure regulator and fuel rail that controls the running ability

Try resetting the ECM, turn the ignition key to the on position "engine not running" and pull the fuse to the ECM and place it back in. Leave the keys in that position for 30 seconds and then turn it off and on again for 5 seconds and start. this will reset the ECM to default. It may stall again but let it, just start it again and let idle for 3min and go foe a test drive. This should reset the way the engine and transmission performance, and should reset the idle issue on your Envoy. Good luck and keep me posted.

start by changing your fuel filter

IAC motor, or dirty throttle body.