2003 Chevy Blazer Engine has no power

I have an issue I'm stumped on. 2003 Chevy Blazer LS 4.3L SFI OHV with 80,000 miles SES light on. The engine is running rough and makes no power. It idles pretty well. But when you give it gas it bog's down. Sounds like it is choking on itself. Rev the engine to 1,500 rpm doesnt go any higher then 2,500 and then it nose dives. Banged on the catalytic converter nothing is rattling. Checked fuel pressure. Fuel Pressure is constant between 55 - 60 psi. When I scanned it DTC codes PO101(MAF), PO128(Coolant Temp Sensor/Thermostat), PO756(Shift Solenoid B), PO300(Multipal Cylinder Misfire Random). Replaced Distributor Cap, Rotor, Spark Plugs, Wires. Replaced MAF, Air Filer (PO101) and Thermostat (PO128). Cleared the DTC codes. The engine sounds a little bit better. But still the same thing no power and SES light still on. Scanned it again. PO300, PO128, PO756. No vacuum leaks that I have detected so far. I thought about changing the TPS. But it seems like all I'm doing is throwing parts at it. And not actually solving the problem. I called the dealer about the EGR Valve and they said there is no replacement part it doesn't go bad. I find that funny and hard to believe. Could the shift solenoid and coolant temp sensor be causing all these problems??? To me it doesn't sound right.