1990 Frod F-150 with 152,000 Miles

I have a student in my class who is having trouble with his truck. The problem is a very rough running engine below 2000 RPM. Anytime the engine is below 2000 RPM is has a big hesitation, backfires, and chuggs. Once you get the engine to get above 2000 RPMS then the engine smooths right out nicely. We have tried the basics like fuel filter, plugs wires, cap, and rotor with no luck at all. I was able to perfom a diagnostic test on the truck, and with the key on engine off it popped two codes. ONe was number 22 and the other was 32. I think that #22 was MAP out of range and #32 was EGR not seated, but I am not 100% positive if that is correct. If it is correct, not sure what that is telling me. I hope that this is enough information, and I would appreciate any info to help me out.