power loss 1-3K rpm, needs tips on how to trouble shoot. Options

[tod914]

Car is a 75 2.0 fuel injected w/55K miles. Here is what happened. I took my rear calipers into a "reputable" shop to have rebuilt. When I reinstalled them on the car, one of them leaked. I was really pissed off and had the car towed into the shop. They were told to fix them. They had the car for 2 days "testing" and repairing the brakes.
When I brought the car in it ran fine. Plenty of power.
It was in need of a muffler due to rust and a small hole on 1 side. But, it was fine to drive. After about 30 miles of their "testing", they blew out the side of the muffler and the car really lacked power. I attributed the power loss to the muffler. I replaced the muffler with a bursch.
A fair amount of the power came back. However, there is a deadspot from 1-3K rpm. My friend did a leak down test; less than 10% on all cyls. He adjusted the valves and repaired the torn mps diapram (which i will need to replace at somepoint). the mps repair made the car idle smoother. He did not adjust the mps.
What has been done to the car; new fuel pump, lines, fuel pres reg, head temp sens, plugs, wires, fuel inj triggers, rebuilt aar from aa, new coldstart, pertronix ign., cap, coil, new throttle switch. All these components where put on before this incident.
Any tips on where to start trouble shooting would be great. Needless to say the shop was not paid. My guess is they either beat the shit out of the car or intentionally messed something up. Im in the process of writing a letter to the shop owner. Meanwhile, I would like to get the car running correctly again.

Thanks