I know time and money are not always abundant you need to have a base line when trying to find out whats wrong. I see that you did the fuel filter you also need to take a look at the Air filter and the spark plugs and wires. If you have the history on them then fine if not you may want to replace them look at the plugs do a google search on how spark plugs pics. They should all look the same white or a little tan on the insulator.
If replacing them go with the double sided ground not doing this can cause issues. When putting them back I use a Torque wrench the last thing you want to do is strip out the threads in the head. (HF have a decent torque wrench really cheap or borrow one.)
Checking fuel pressure is a bit involved you need to search some one out to help with that or take it in to a shop. Keep us up to date