my trans jumps a few times when going into 4th from 3rd gear. is this shudder? i have a 98 f150 4.6 4x4 112000 miles 33" tires and superchips 1715 tuner. what should i do to fix this?

also, i tow a 4000 lb boat every couple of weeks should i get a shift kit? which one? i put a trans cooler on it a few weeks ago.

thanks,
chris