Truck Repair: 96 6.5TD with 3 trouble codes, many different things, auto parts store

Question
Got a 96 C3500 6.5TD with 200k miles on it.

This morning I started it and drove about 3 miles before my sevice engine soon light came on and it started to run real crappy.

I was able to limp it to the local auto parts store where they used their scanner to pull up the OBDII codes. PO251, PO335 and PO370.

But they could not tell me if one or more things went wrong with my truck and told me to have it checked out by a mechanic :(

Odd thing is the cruise was working before the trouble light came on the first time and then it didn't and it worked after the parts store cleared the codes and ran fine but after about another 5 miles the light came back on and the cruise failed to work again and the truck ran like crap.

Knowing that a simple sensor can cause all kinds of trouble I would like to know for sure which one needs to be replaced before I waste my money on too many different things :) Thanks in advance!!

Answer
well after checking the codes they all point back to one thing po335 crankshaft pos.sensor since the others are affected by the the c.p.s this is what i would change first and you can pick this up at autozone for about 40.00. thanks for the question and if you need anymore help just let me know.