cars still loosing power starting around 3500rpm

[crazy5.0]

I took the car t omy local mechanic and he says the car is probable running lean at higher rpm's. He recommened that I get a adjustable fuel pressure regulator and a in the car fuel gauge. I'm not gonna do anything at this time. My car had been running weak for over a year and a half. I'm just gonna buy another stang,perferable a notch and swap mytrans,driveshaft,rearend,lower control arms. My car looks like crap and still needs front lower control arm bushings and softer struts and shocks, the ride is extremely harsh and has no weight transfer. The bumpers are yellow gray and the blue paint looks very faded in the shade. Sorry to rumble on about my car, but I hate my car most of the time. I had to pay $285 in diagnostic work over the past 3 months and nothing was fixed. I'm tired of spending money on my car.
Thanks for the help anyhow.