93GC Problems ANYONE?

Ok I have a 1993 Grand Cherokee, I have a couple of problems maybe someone here can help me. First off, the transmission. Shifts very sloppy at times. slow shifts when it does, doesnt want to shift alot of times, have to let off the gas to get it to shift. then when it isnt having any of the above problems it shifts thru the gears really fast. Any ideas on this one? Second is the oil pressure gauge is going psycho on me, starts up and goes to 80 then down to 40 then bounces while driving, never did this before. third is the engine seems to be missing really sitting at a stop you can feel it miss. changed the plugs cap rotor everything in the distributor. the truck also gets VERY VERY bad mileage. we are talking 200-250 Miles to a full tank of gas thats a 25 or so gallon tank. on top of all that it PINGS, REALLY bad.... PLEASE help anyone have any ideas where to start... i have been reading and see that the TPS might be the shifting problem. IS that possible? thank you in advance...

Jackie