just got my first cummins about 2 weeks ago. its a 99 2wd bone stock 2500 with 169xxx miles. loving it so far but the last couple days its been acting kinda weird. with light acceleration between 40-45 it jumps about 200 rpms and then drops back down to normal. between 45-50 it only does 100 and 50-55 it jumps about 50 rpms. but when it starts if i give it a lil more gas it doesnt do it. what could it be? i havent done much checking bc i thought it would just wear off and stop doing it. as far as i know its the stock fuel pump also...an elderly couple owned it before me and used it to pull their travel trailer

 

its hunting for gears