1994/2000 Suburban 4L60E PROBLEMS

I have a 1994 Suburban w/5.7, 300,000 Plus miles, Original engine,  and the original trans gave out some time back. I ran across a low mileage 4l60E, but it was out of a 2000 Tahoe, with supposedly 45,000 miles, I bought it, got it home, despite a lot of difference in overall appearances, it bolted right up, plugged right in, and I just had to move the Crossmember back and drill one side of the crossmembers holes to bolt the crossmember back in. Trans worked fine, but I never did feel the convertor lock up like it used to, since making the swap. Otherwise it worked fine, I just lost some gas mileage.

That was several years ago. Don't use the truck much, maybe have 2000 miles or so on it, since putting it in, used it this past weekend, trans seemed fine, but I had a whine while running which I thought was a alternator bearing, pulled over checked all fluids to be sure, all was well. Got into it the next day, whining got much worse and the trans started slipping, whining is more pronounced now. Getting ready to pull the pan to see what's up, hoping that the filter is clogged and maybe it's salvageable.

Sound familiar? Any ideas?

I only use this truck to haul my boat, or to take my Boys scout troop to an event or pull the troop trailer. Its always had a aftermarket trans cooler on it, flushed it before the swap, everything has been fine til now.

If using this later model caused my problem to occur, I'm hoping someone can tell me so, as if I have to replace it again, I don't want to make that same mistake again.

Thanks!
Bob Lemley
Findlay, Ohio
419-722-2533