Timing question

My 92 eclipse 1.8 l started running low on power fron one day to the next, took it to a mechanic and he said the timing was off and he reset it. Car runs better but still low on power. Any ideas? Could the timing belt slipped to cause this, if so will I have to replace the belt again?

Low on power may be damage already done due to the timing problem. Also if it is the timing repeatedly going out then you MAY want to look into a new tensioner pulley if it has one a weak tensioner will allow the timeing to shift. You shouldn't have to replace the belt if you just did unless it's jumping teeth and not just shifting. And if it's jumping teeth then you've got bigger problems than just the belt.

OK so the thing to do now is to put it at TDC, replace the tensioner pulley and realign everything and retime it? I ran a compression check and it's within limits.

Check the tensioner first no need in replacing something that's not bad. Try moving it by hand it should have no play in it whatsoever. Also you might want to check your vaccum advance system see if that's possibly causing problems or even possibly something with the computer adjusting the timing also. But the easiest thing to check will be the tensioner pulley.