I ave a 97 c1500 with a 4.3 and an automatic transmission. Just under 160k. i have a pretty strange problem with the transmission. after i drive around 30 miles, shifting from 1st to second it slams into 2nd. if i restart the truck it shifts fine. its wierd because normally it shifts as smooth as a brand new truck. Im thinking do a flush and filter change. Im just cofused on this one because like i said when you restart the truck it wont do it