Drastic reduction in power uphill G30

[golly G30]

Have a 95 G30 5.7 Vortec with 114,000. Use it exclusively for work; picking up large loads of equipment. Yesterday it struggled going up a hill with a small incline. The drop off in power was extreme; could not get initially go beyond 15mph and then had great difficulty passing 35mph. The RPMs seem to flatten out and it would moan to shift into the next gear. On flat surfaces and going downhill there were no problems. My total milage for the trip was 600 miles. It happened before I picked up a load and after; load is about 2000 pounds. If I had to guess, it seemed like it happened more before the extra weight. Last week I was driving through the Blue Ridge Mountains and it acted like usual; a real powerful beast. Seems like there could be a number of potential causes from fuel to vacuum to transmission. The check engine light flashed briefly for about a minute and it never came on again. Much to my surprise, I averaged 15mph. It never stalled or failed to start. The idle seemed to be a little high, though. What does the forum think?

[Blue Bowtie]

Without more data the diagnosis is going to be difficult. Air flow is the first suspect, between both the intake tract and exhaust system. Fuel flow is another question, but inadequate fuel flow or pressure would likely have set a DTC and probably several due to the resultant lean condition. Weak ignition is another suspect, but it is very likely that a DTC would have been set for misfires and cat converter performance.

It would be good to connect a scanner and read the stored AND pending error codes.