If you are indeed burning a lot of oil, you may have plugged up your new(ish) cat. Sounds like you need to do a compression check. If that's OK, then I'd start looking elsewhere.

I've been burning a lot of gas in my '86 for the last few months. I had some stuff apart for other maintenance and noticed that one of the rubber intake tube elbows had a crack in it. I repaired it with some Household GOOP (aka Liquid Nails, Shoe Goo, etc.) and it runs a lot better now. Check those intake parts pretty carefully. The crack was pretty tough to spot unless you pulled it apart to open it up.