Rear diff. locking under acceleration...type 44

[Mikea2769 at aol.com]

Before I start probing around...anyone been there?

On my 87 5kcstq, I noticed a few months ago that upon hard acceleration, or 
going uphill the rear diff light would come on and then go off immediately 
after letting up on the gas. Now it seems the diff is actually locking-I can feel 
it kick in, then after letting off the gas it now takes a while before the 
light goes out, and i can feel slight "kick" as the diff unlocks. I tried another 
dash switch from an OK vehicle-no change. Any guesses where to start?

Mike Aiello
87 5kcstq, 302k miles, orig. owner