a518 2nd to 3rd shift problem
 

So I start my 1991.5 d350 and drive down the road and the first few 2-3 shifts are fine but it usually seems like the third or fourth 2-3 shifts it hangs up in 2nd untill about 40mph and then will finally shift into 3rd and then it doesn't seem to hang up after that. What do you guys think I should check, could a simple trans service fix this?

Simple service, adjustment, and a bottle of the thick Lucas transmission additive should fix that. It's from an internal leak pressure loss and the thick Lucas will really help.

check your TV cable (kick down) at the trans. Mine has a tendency for the linkage to come off there.