1998 Suburban 4L60E with ~70,000 miles on the rebuild. The PO had the trans rebuild by a trans shop I have the receipts somewhere. I will have to double check but I think the converter was replaced at that time.
Last sunday I was towing my mustang home from Bowling Green to Houston. About 7 hours into the trip after stopping for gas their was a horrible high pitched screeching sound from the transmission in 1st and 2nd with the engine above 3200 rpm (accelerating up to highway speed). I know these 4L60's are fragile so I just towed the whole way in 3rd gear no OD used. When the screeching sound happens it also felt like the truck stopped pulling/accelerating as hard. I don't know if it would make the screeching noise in 3rd because I did not drive that fast I didn't run more than 3000 rpm in 3rd. I wasn't hammering on the truck just between 1/2 and 3/4 throttle while accelerating up to highway speed but once the noise started I would just let out and the trans would up-shift noise would go away and I would continue to accelerate. This continued for the rest of the trip.
After the trip driving around town empty no trailer I can run the engine all way to the redline in 1st and 2nd and up to 4,000 in 3rd no abnormal noises and the truck accelerates the whole time. I drive it to work daily and have not had a bad shift, or a slip or anything strange.
While towing when the truck stopped pulling it did not feel like the transmission was slipping, the engine rpm did not change just stopped pulling.
When hearing the noise while towing my initial thought was noise coming from the converter. After noticing that the truck stopped accelerating but it wasn't trans slippage also made me feel like it might be converter.
Any ideas? I probably won't be towing anything for a few months and then it will just be local.
Scott
