Chevy S-10 thumping

I just bought a (11/87) which is a 1988, Buick Regal Custom, 2.8 Multi Port FI. The problem is when i get up to about 45mph the car chugs, when i let off the gas pedal it goes away. This car has a loud Tapping noise at the top of the engine. Possibly a lose tapit. They told me that the car did have an oil leak but they took it to the shop and they fixed it. I do belieave they said they gave the car a tune up. They took the car in to get an oil change, i changed it again because the oil was thin (5w10). Another problem is the oil pressure gauge reads no pressure. When i open the oil fill cap i can't see any oil at the top of the engine. If this car does blow up that is no problem, I have a 1988 Olds cutless ceria that i can swop engines with. Should i clean out the throttle body with carb cleaner? i also forgot to mention that the antifreeze in my car is black. what happened? it still heats great though. suggestions any one? thanks in advaced

I have this 1991 Chevy S-10 pickup, 4.3L with 80K miles, that has sat for about 2 to 3 years without running, but have now decided to put it back in business. I did all the normal stuff, changed out oil and tranz fluids, air filter, fuel filter, cap and rotor, wires, plugs, battery, flushed radiator. After all that, the truck sounded and ran great, revved the motor sounded good. So, I went out and started it every few days while I waited for the plates to arrive, ran good. After I was legal, I drove it 5 miles, when I got to my destination, it began to run real rough and sputtery. I checked the throttle body, both injectors(?) are spraying very nice and even with no dripping. When I gave it gas it bogs down but I had to flutter the gas to keep it running. I checked the exhaust coming out the pipe, it was VERY hot, couldn't keep my hand even a foot away from it. When I gassed it, I felt what can be descibed as "little black fine rocks" shooting out the pipe every few seconds with a little bit of smoke. I'm not a mechanic by any means but could the catalytic converter or the muffler, be plugged up and rusted inside, causing the superheating of exhaust and and these "little fine black rocks" are rust? The catalytic gets hot but its not glowing hot. Could it be its bogging down on its own exhaust because it cant get rid of it quickly enough? I think I can test out my idea by, just disconnecting the exhaust, before the catalytic, to see if that is it, but its 20 degrees in the garage and the bolts on that catalytic ain't gonna come off easy. Any ideas, I would appreciate if there is anything I can do before possibly wasting my time disconnecting the exhaust.