I have a 2001 4.6 with the 4r70w. It has 180k kilometres (110k miles). If I let off doing between 30 and 80 for a few seconds, then get back on the gas it bangs, don't think it shifts, just feels like slack. Also sometimes on the highway when I kick down to third up a hill, it will not go back into forth no matter how I use he throttle, even backing right off for a few seconds at 120kmh, it usually goes back to 4th if I put the cruise on for a second or two. I checked the oil, it's clean but a bit overfull. Would it just be a flush and filter that would help? Or is this an actuator or relay problem? Thanks!

 

I would start by getting the right amount of fluid in there, Crawl under the truck and see if things move that shouldn't, or things that shouldn't move but do. In park try and spin your drive shaft, then try and wiggle it. Maybe your U-joints or your gears are giving you the thump.

 

Ya checked all that. U joints and output shaft bearing are good. It feels like the banging is maybe in the torque converter, feels like it's not engaging and when I hit the gas it grabs all at once instead of acting like a clutch.

 

Try to grease the slip yoke.

Is it one solid thump or more of a shuddering? If it is a shudder get some of this to pour in the trans fluid. If it solves your problem your torque converter is going out.

 

Ya it only shudders slightly accelerating from a stop and only for a bit. Probably just the converter. Not used to the whole "automatic" transmission thing. This is my first auto vehicle ever so not really used to the symptoms lol, thanks for the help!