01 Powerstroke runs good then loses power

[JRodrick]

I'm new to this fourm and I just bought a 01 7.3 with 116k miles. Before I bought it it had sat for a year. I drove it home and after about 10 minutes of driving it slowly lost power to where I could have it floored and would only be going about 5 mph at 400 to 500 rpm. I got it home and changed the fuel filter which was filthy and cleaned the bowl. Tried it again and did the same thing. It was sitting at an 1/8 th tank and I was told they sometime won't run under a 1/4. Put ten gallons in and brought it to half and ran it again and it did the same thing. I have no clue what would cause it but it sounds like its starving for fuel but no sure. Anybody have any ideas?
Thanks

[Turbostang500]

Pull fuel filter cover and drain the bowl with the yellow lever on the back. Now have someone turn the key forward and you watch the fuel bowl fill up. It should fill up in about 10-15 sec. There is a coating inside the tank that can block the pickup. If that is good, check the tps on the accel pedal.