MIL/PCM/DTC issue, about to go on long haul trip.

[C.Gift]

*Quick Summary on bottom*

Hello,

I'll start out with the truck. It's a 1997 F250 SuperCab Long Bed 4x4 XLT, 239k on it. I have an S&B intake and a 4.5" straight pipe. It might have more modifications internally and electronically, but I'm not sure, because the original owner was a diesel shop owner and didn't document his changes. The biggest and most relevant problem child is that supposedly he has a tune on it for economy, but I can't find a chip anywhere (have yet to take out the PCM though). Which leads me to my problem.

I brought my tools home after leaving my last job, and decided yesterday to plug my OBDII scanner in (the warning light wiring harness has a short so I don't have a check engine light). I didn't pull any codes, but the scanner told me that my MIL status was 'on'. So that leads me to think that I have a Powerstroke-specific code. The truck has been running fantastically, I haven't been smoking, no rough shifts, now and then a rough idle in the morning when first start it, but nothing that concerned me. It has lately been running pretty rough when I go into reverse. I'm an entry level tech, but this is confusing the crap out of me .

So basically, here's what I need help with: I'm wondering if I should run it back to my old work and have them hook up the Ford computer, or if it's nothing to worry about. I'm loading it up tomorrow to make the move to Sandpoint, ID from Arizona, and would really hate to be stuck on the side of the road in Utah or something.

Thanks for your help!

PS Here's the quick summary:

-1997 F250 4x4 239k
-MIL on, no generic codes
-Major trip-killing issue?

UPDATE: The reverse issue is torque converter related. I think I figured it out, probably an air temp sensor issue from when I installed my intake. Fingers crossed...