I drive a 2002 2500HD with right under 150,000 miles. Its a 6.0 liter with the 4l80E. I'm wondering if the transmission is just worn out and slipping. I have tried to spin the tires on wet concrete without much success, and no success at all on dry pavement unless I am moving and turning.. It also seems like it wont accelerate as hard off the line as in the past. Also, when im cruising around town stop and go, when i let off the gas it their is a thud sound from the transmission. It does it even louder when held in 3rd gear. Any suggestions?