I recently purchased a 2002 1500 hd 6.0 4l80e 4x4which had the transmission burnt out of it. Transmission was rebuilt and also did the valve body updates. Transfercase is the 246 which when I got the truck looks like it was recently replaced before I got the truck with a remanufactured unit. Everything worked fine for about 4 days. Now intermittently when the truck shifts from first to second under a light acceleration it gets a clunk then a slight slip or hesitation, I would say hesitation cause rpm doesn't seem to go up much if any, then another clunk then goes into second. That is the only time and gear change it seems to do it. I never run truck in auto 4x4 only in 2x4 of 4x4 and it doesn't seem to make a difference. I did check the rear end and spider gears and everything seems to be ok, even the junk gov lock (never liked them). also when in 2x4 the front driveshaft turns hard like its supposed to. according to gm it shouldn't spin freely and could take up to 40lbs of force. don't think its that and all mounts are good. Talked to the trans guy and he said that it could be a sticky accumulator. I am supposed to test drive and scan tomarrow and hopefully I will know. I am just curious if anyone else has had this problem or has an idea about whats going on. I found a tsb for 03 and up trucks with 4l60e about a wire going to the alternator which needs re ran but my truck is an 2002 with a 4l80e.