89 K2500 stall

Hello everyone,
Been away from the older vehicles for a while, and need some help.

I have an 89 K2500 with a 350K motor that stalls in gear at Idle.
IAC counts start at 55, then when in gear, count down until below ten, then stalls. MAP reads 1.7 in gear, and 1.2 in neutral. If I open the throttle slightly, it will run in gear. Any Idea's? It runs perfectly except for this glitch.

Thanks for your time.

Welcome to AF. Clean the throttle body, iac and iac passges. make sure no vacuum leaks especially around the throttle body base.

Thanks for the quick reply.

Removed throttle body, and cleaned what little carbon was there.
Inspected gasket, and found no leaks. MAP reading is good, so I don't suspect vacuum leak. Could the distributor somehow lose voltage at low rpm?
I'm below 600 when the engine dies, what should idle rpm be in gear?

Thanks again.

About 600 in gear, the iac sounds like it is not responding assuming the engine runs ok besides this issue.