My 2001 CTD that I pull with every day with 250,000miles is experiencing transmissions problems, what is happening is it will shutter(like a slipping TC) when accelerating & in 4th if I slow down to about 80KM/H and accelerate to 100KM/K and beyond the RPM will jump about 100 then lock then another 100or 200 then "grab" again. I can visually see this with my tack and I can hear the motor. What do you think it going on? The only mod it an EZ. I think its the TC slipping,if I do the TC should I do the VB as well?
It shifts no different.

 

Sounds like the TC to me as well. If you are pulling daily, I would upgrade the VP with the TC (to get more pressure which means more holding power).