'88 4.0L power loss...

I have an '88 Cherokee, 4.0L, Auto, 4wd, 31" tires, 3" lift, about 30k on a rebuilt engine. Runs fine around town and 4-wheelin until I run up any sort of long rise, hill, etc. It will slowly lose speed until kids on tricycles and small birds flying into a headwind are passing me. It will kick down into lower gears but will still lose speed eventually. And not just slow, I mean slooooowwww. No power at all, but only on long hills.

It has almost all new sensors (TPS, CPS, MAP, O2, idle motor), new exhaust including manifold, K&N filter and tube, plugs/wires, cap-rotor, and coil are all new. Injectors are Ford 19# 'ers and cleaned.

It is running a bit rich and my mileage has dropped by about 4 mpg. I have checked everything I can think of and am hoping there is something I've missed or maybe someone has another suggestion besides selling it and buying a '92 or newer to get the HO :)

And if anyone is ever out in Anza-Borrego area drop a line. Going out to Indian Hill weekend after this...

First, how long a hill? How steep? If you manually downshift, does it still lose power? Does it do it when the tank is full or 1/2 full, or close to empty?

First, how long a hill? How steep? If you manually downshift, does it still lose power? Does it do it when the tank is full or 1/2 full, or close to empty?
It runs up short hills fine. On the freeway it will run along at 70mph with no problem, but, as soon as the rode starts to rise it will start to slow. The rate of slowing is proportionate to the grade/length, but, it's not just that it goes a little slower, on long, steep hills it slows down to about 20mph.

I can downshift manually and it will pick up speed, but it will eventually slow down. If I floor it and force it into passing gear it acts the same.

It almost seems as if there is no advance on timing.

And, a rather important thing that I forgot to put in yesterday; at high rpm's (like when it's floored), the heater vents would close. I messed with some vacumn lines and the canister and it quit doing it. I couldn't find any vacum leaks tho.

Fuel level doesn't have any impact (on a side note, haven't changed the fuel filter yet).

Making me more nuts than I already am...