American Motors: 73 gremlin is sick (not the good kind of sick), simplest thing, distributor cap

Question
my little gremlin is old and tired. it's all he can do to climb long hills, and sometimes he'll backfire out of the carb when trying to get up said hills. what's that about?
and (yep there's an and)
in park and neutral he idles @1200 / in all other gears his idle rpms drop to 700. what's that about too?

p.s. i'm kinda dumb

Answer
The simplest thing to do is to replace the carburetor. Sounds like yours is in need of an overhaul or replacement.
While you're at it, has it had a good tune up lately? This would include spark plugs, ignition points, rotor, distributor cap, ignition wires, air filter & fuel filter.