Need help GL Wagon EA82

OK....I'll give you all the long story. Bought an 87 GL wagon, nice condition, sat without running for 4 years.

Bought it, added some gas to carb, jumped old battery and drove it home. It barely made it up hill from town, clacked, like a valve slapping, really badly, not much power.

History: Old owner was told she needed another engine, small shop in a small town changed it with one from JY. I found a package in the rear storage compartment with a timing belt in it? Wonder why.

I decided to back off the timing and see if it quieted down the valve clacking. Found I had to back it off as far as it would go. Drives OK. New plugs and wires and about 12 miles a day for the last 2 years.

I have a feeling the shop did something incorrectly in regard to the timing, I have no light to check it with. I can remove the timing covers if needed to see if the timing marks are correct. I did find the small flywheel inspection cover under the back seat?

Now it seems to stumble when trying to climb a hill, gas mileage is really poor and the only time is seems fine is idling and revving.

Any help or suggestions would be appreciated. There are also several vacuum lines in and around the engine compartment that are plugged off. May or may not be an issue.

I am sure the engine is an EA82, but maybe a different engine was in it before? Don't know.

Thanks in advance,

David