Subaru Repair: 1991 Legacy power loss under load, auto electrician, legacy power

Question
Hi there, i have a 1991 liberty stationwagon auto 2.2l here in australia (legacy in the US i think )which has us slightly stumped. The problem is that when climbing steep hills it will drop down in gear under acceleration which it should do however as the hill gets steeper it will drop in power and vibrate( similar feeling to an untuned car). Once you get to the top of the hill and stop eg say at a light, the car will seem to 'reset' itself and the vibration will stop and the car will appear normal and operate normally as if nothing is wrong. ( by reset i mean that the revs pick up and the vibration stops as if someone just snapped their fingers). in attempting to solve this problem we have:
Changed MAS, plugs and wires, fuel pump, fuel regulator. Checked ignition coil, sensors, eg knock, camshaft, crankshaft. The fuel injectors were also taken out and cleaned. I had also replaced the transmission 2 years ago.Some of these changes helped the car run smoother however didn't fix the 'power loss under load' problem. My mechanic and auto electrician are of the opinion that the EMC may be faulty ( which isn't cheap). Would you agree? and with your experience could you pinpoint any other possible culprit.
Thanks Sam  

Answer
You my friend have sticky valves.Very hard for the average mechanic to correctly diagnose as mechanical problems are not usually intermittent.What happens is that sludge builds up in between the valve guide and valve stem and under increased load situations the valve or valves will hang open momentarily causing a cylinder misfire and lack of compression.Here is the only thing you can try short of a valve job.
have a engine oil flush,change and additive package such as one offered by lube guard.Use high quality synthetic or synthetic blend oil.The cleaner should help with the sludge the additive should help keep things slippery.Also have a fuel induction service done as well this will clean the valves up some also.

Hope that helps

Justin
All Wheel Drive Auto