Intermittent power loss

The truck was sitting out in the cold for about two weeks. We saw a leak in the heater hose which leaked into the throttle position sensor. We replaced the sensor and replaced the hoses. When we went to use the truck 10-30 minutes into running it at highway speeds we encountered power loss. It did not stall or quit running but it would go down in power to 20 MPH. Tried the overdrive switch and switching tanks with no improvement. We have replaced the computer, dropped the front tank and visually don't see anything but did replace the filer, which was not clogged. We put a new EGR valve and solenoid, distributor pick-up, EGR vacuum control, replaced all vacuum lines (used diagram under hood) also the exhaust manifold. We replaced the MAF but took it off as it even ran worse. We are at our wits end as this truck has never given us a bit of trouble except a pan gasket a couple of years ago. Any help greatly appreciated.