Did you check if there is a Centerforce Dual Friction for it?
Is that NV4500 have the 6.** granny low or the 5.**?
I'm sure you have secured that 5th gear, correct?
Matt,before you go any further i would check your compression to see if you have any tight valves if all is good check your firing order including your injector harness output,you could also do a running compression test for individual cylinder output. If you could pull out the injector rail...