"Well my Blazer is going downhill FAST. This weekend I put on a new EgR hoping that would fix the problem of poor acceleration and knocking. Well it didnt. But with it plugged in the acceleration was MUCH worse. So I unplugged it, and the knocking got worse but the acceleration got better. "
First questions: How many miles on the vehicle? Has it been overheated recently?
The EGR system is designed to pass a calibrated amount of burned exhaust gas back into the intake manifold to be burned with the incoming air/fuel charge. The main benefit of this is a lowering of the combustion chamber temperature. A non-functional EGR system will make your engine more prone to overheating, detonation and pre-ignition. You will also probably fail an emission test for exceeding nitrogen oxide limits.
Having said that, just replacing the EGR valve will not always fix a problem with the EGR system. Many times the EGR passage is already clogged by the time the valve gives up, leaving you with another problem that is best fixed by pulling the intake manifold and clearing the passage.
It is possible you have burned up a bearing. It's also possible you didn't install the EGR valve correctly and you now have a nice exhaust leak under the hood, which can sound a lot like a bad bearing.
One way to test main bearings is to put the car in drive(automatic) or
4th/5th gear(manual), hold the brakes, and apply a SMALL amount of throttle/clutch to raise the engine RPM and put LOAD on the engine.. Raise the speed about 200 rpm at the most. A knock that becomes progressively louder(to a point) would suggest that you have one or more bad main bearings. Of course if you have an exhaust leak all bets are off. How to tell you ask? Start the engine when it is stone cold first thing in the morning. Start passing your hand near the manifolds, the connections to the downpipe, and the egr valve. If you feel any pulses you just found a leak. Look for a black streak near exhaust connections, the presence of any would likely indicate gas is escaping at that point.
It's also possible the EGR valve is leaking when it opens, and it is not supposed to be open at idle. On the newer GM computer controlled EGR valves(the $300 ones...) I don't know how to force it open to test it. The old style, you use a hand vaccum pump. You will need to have a helper open the throttle slightly, if you open the EGR at idle it will stall the engine. What you want to look for is abnormal noises when the valve opens indicating that the exhaust is leaking OUT of the valve instead of getting sucked into the intake manifold.
I am assuming you did not do your oil change and radiator flush. I hate to say it, but I've never had a positive experience with a mechanic. Ever. They always manage to fix one things and break two others. I would suggest replacing the oil filter immediately if you choose to do nothing else. Cut the old filter open and inspect the filter element. If it is full of metal shavings you just confirmed your suspicion about 'burning up your engine".
Good luck with it,
Chris