1997 Chevy Truck No power on hills

I have a 1997 K1500 with the 305 motor. I got it about a year ago. This thing has no power going up hills. If I kick it down to 2nd gear it goes till it hits 45, drops to 3rd and then just goes blah. The RPM's drop and I start crawling till I get back to 2nd gear again. It's fine out on the Interstates, I loose a little speed but nothing bad but on the back roads it's a pain.

No check engine light, had a scanner on it for a 10 mile ride including big hills and nothing shows up. Plugs, wires and distributer cap are new within the past 3 months and made no improvement. Fuel filter has been changed out twice in the past 15,000 miles and the air filter was also changed out.

Any ideas?

Thanks

Tony