Diesel Bombers - lack of power, new to diesels

I have a 1986, f250 with a 6.9. Never having owned a diesel before its been a learning process. The problem I'm having is that it seems weak, when I first got it it was a mess. So far I have replaced the muffler, (took the car muffler off) replaced the glow plugs, put a manual switch on because the controller was fried. Changed both air and fuel filters, cleaned both fuel tanks. It runs and starts fine, but it barely pulls itself up hills. I have a heavy trailer I would like to pull with it but it just doesnt have the power. As I asked around, one guy asked me if it would "blow black" when I stepped on it. I tried it and it doesnt really blow anything. He said it was probably a fuel related issue but didn't have any suggestion other than take it to a mechanic. Besides being limited on funds, I'm not the kind of guy to pay for something I could do myself if I have the proper info. Reading through some of the forums I've seen talk of turning up the pump, but I assumed it should be set right from the factory unless someone changed it. If anyone could give me some info on what to try first I would greatly appreciate it. Someone also mentioned a screen where the fuel line enters the pump may be clogged. That is the next thing I was going to check. Also can someone tell me where I can get a diagram or info on the pump. It would be helpful to understand how they work.

Thanks,

DRAPP127