I have noticed that my trans will shift very hard sometimes. It does it only when I am accelerating hard. Just now when it went to Overdrive it was loud and hard shifting up. Did it before in lower gear, so hard I thought I hit something.

Truck is a dually and is stock except for exhaust. No chips

 

Sounds like a worn/sticking line pressure modulator in the Accumulator Valve Body. Fairly easy fix.

 

Thanks, I will check next time I drop the pan. Any good YouTube videos on fixing that

 

None that I am aware of, but here are the instructions for the Sonnax replacement. http://d2q1ebiag300ih.cloudfront.net...f?v=1431631113 I use the .427 diameter one (third one down), part# 96948-01K
Here is a simple shift kit that includes it. http://dieselinnovations.com/4r100-s...lator-kit.html Wouldn't be a bad idea to change the accumulator springs, also. This kit is not too aggressive.

 

http://http://d2q1ebiag300ih.cloudfront.net/uploads/instruction/file/527/36948-19-IN.pdf?v=1431609325
Found this also. Nice Tech help

 

Not that it couldn't be a problem, but I haven't seen any trouble with that piston on any of the valve bodies I've dealt with. The only other thing I like to change is the accumulator regulator valves. They have been know to stick and cause shift problems. TransGo E4OD/4R100: E4-VL-LR3 I see they new include a stock .372 line pressure modulator valve in this kit.