When u put my truck in reverse or drive sometimes it will kick hard before going in gear. It's really annoying. It doesn't do it all the time so I know it's not suppose to do it I just don't what could be causing the problem. It feel like something may be sticking in my valve body but I do t know alot about transmission. I have also read about u joint. I just need some guidance in the right direction. It did it bone stock, before I did any modifications.
Harsh engagements into Drive (or Reverse) are annoying, but typically they are not a durability concern (the engine torque at idle isn't high enough to do any significant damage). Clunky / banging engagements may be due to worn U-joints, or high engine idle speed.
Another factor may be the length of time the engine was shut down before startup, or whether (or how long) Reverse was engaged (before shifting into Drive). On a Drive engagement, the UD clutch is the applying clutch, so it controls the smoothness of the shift. The primary adaptive (learned) value for UD clutch engagements is the UD Clutch Volume Index (CVI). Actually, there are several UD CVIs, including one for "normal" Drive engagements, and one for "1st" Drive engagements (1st engagement after startup, or after shifting out of or past Reverse). When the engine is off, fluid can slowly drain out of the UD clutch, so the volume of air in the clutch (that the CVI value has to compensate for) may vary depending on how long the engine was shut down. Let's assume that the "1st" N-D UD CVI is set to compensate for a fully drained clutch. If you make a quick stop at a gas station or store (just a few minutes), maybe the UD clutch doesn't drain down all the way, so when you restart and shift into Drive, the CVI is too high (it assumes you need more fluid to apply the UD clutch than you actually do, since the clutch is still part-way full). That could give you a clunky / harsh engagement.
So pay attention to the circumstances immediately before your harsh engagements. Do they happen when the engine is cold, or hot? After a short shutdown, or a longer one? After you've engaged Reverse, or after you've simply shifted from Park (right past Reverse) into Drive?
I probably can't tell you how to "fix" an intermittent harsh engagement, but maybe you can at least better understand what circumstances tend to produce those harsh engagements.