Diesel Bombers - Motor/Tranny acting up. at work need help fast

I posted this here because I'm at work and if possible I need to at least figure out what could be wrong before I get off of work at 3 pm. My truck is an 85 Ford F-250 6.9L 4 speed 4x4. I came out this morning and started my truck, let her warm up and drove clear into work with no problems. I got to work early so I ran to the post office(across town) and noticed that my RPMs weren't quite right to shift. I can't tell you where they were at because my tach doesn't work. At first I thought something was acting up with the tranny which is a 4 speed. On my way back to work, I stopped at the gas station and put 20 bucks in thinking maybe I had run it that low on fuel(fuel gauge doesn't work either). After filling up I had trouble restarting it. I think this was from air getting into the system because I need to replace my injector return lines. Its really hard to explain but the best i can explain it is a loss of power and it just wasn't quit shifting right. Hopefully someone out there can help me. I'll try to get on when I can since I'm at work. I really don't think anything is wrong with the tranny but that's where I noticed something was wrong. Thanks in advance.
Something else I thought of that might be important is that at idle its just fine, rev it, just fine. I only noticed this going down the road.

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Ok, I feel really stupid. It was only low on fuel because after I put that 20 bucks in it did fine the rest of the day.