While driving and it gets around about 1500 rpms the motor boggs down like somthing holding it back but when I push more on the pedal the car goes pass that point and its ok so by doing this all the time I do go through more fuel. When I put say 98 octane fuel from Mobil its goes ok but does fix problem in the long run. What are some things or one thing that could be the problem. Some tips would be great. I did a diagnostic with ford and that would cost me over $2500 for them to fix I hope that i can do it alot cheaper and have the enjoyment of fixing the problem myself.

My best guess would be a blocked fuel filter.
Shouldnt be too hard to check yourself and if it is the problem, I doubt they are expensive to replace.
If that doesnt work, give the car a good service: oil, spark plugs, leads, filters, fluids, etc and work from there.