Stalling

I have a 88 gmc 4x4 2500, It stalls when put into gear.
If I disconnect the timing wire it runs fine at base timing & doesn't stall
I have replaced the distributor about a year ago along with the fuel pump. I just replaced the ignition module but it still stalls & tested the rest of the computer sensors & it all checks out fine. I've cleaned all the grounds & still no change. I also stuck in a reman computer but that didn't help either. HELP PLEASE????

Well i just checked in to find that over thirty people have read this but not one has left any reply with any help in my situation.
I really could use the help.

My 98 Sierra kind of does the same thing sometimes. I find it does that after I have driven it about 30 miles, turned it off and started it 10-15 minutes later. I just replaced my fuel pump, filter, idling belt and alternator and it almost died when I put it into gear again the other night. I don't know what it is. Sorry i cant help but i hope someone can!

I just had my carb rebuilt on my 1985 gmc 5.0l pickup. The guy that rebuilt it said everything checked out great but it stalled out during road test. It turned out that my vapor canister was full of gas. He order a new canister and the instruction said not to hook up one of the vacuum lines. The new canister even had one of its ports plugged from the factory. This is a common problem for older gmc truck. Alldata shows a tsb on the canister dated nov 88. Something about emission system recall on the canister. Looking down at the canister from the front of the truck the left most vacuum line was removed and the port pluuged.
I hope this helps.

OK here it is, I checked everything in the ignition & electrical system.
Everything checked out good.
I swaped the distributor out with one in a 93 chev suburban, The GMC runs great now & doesn't stall.
None of us at the shop could figure out why all the components test good but gave us problems.

Sorry I missed this one.
Take a close look at the mainshaft magnet..is it cracked? Also the pick-up coil is known for causing low rpm stalling conditions

GMMerlin is right the pickup coil was the gremlin in this case, Thanks