Shakes between 2,000 and 2,800 RPM's

I have replaced spark plugs with oem, injectors, pfr, tension-er, and a lot of other stuff to. It is the engine that shakes but only when it idles or when you stop and no the check engine light is not on.

I do not have a testing kit for that and I really do not have the money to get one. Is there another way I can test it? I would not see why it would have low compression because I have got new plugs and wires in it and every one of them are firing like they are supposed to and it drives fine with no problems, except when it reaches final gear in overdrive and hits cruising rpm's between 2000 and 2500 it starts kind of shuddering. I guess you would call it but I can apply gas or take my foot off the gas and it stops. But it jerks a little when in reverse and it will blow some white smoke but once I put it in gear it stops. It idles fine, besides it acts like at times but not all the time it surges and the battery gauge will start bouncing once I take off it stops.

I also have another question. I am loosing coolant. I have fixed all the leaks external of the motor and I am still loosing coolant. There is none in the oil, the transmission fluid is fine, spark plugs look good, but I have to add coolant ever five to six days. I am not blowing white smoke except on when I put the car I reverse. When I first crank it up and put it in reverse order I make a quick stop at the store run in them in run out crank it up and put it in reverse. It does it it does not smoke when I am driving. Reverse shakes really bad but not all the time, sometimes it is smooth running in reverse, but it still smokes when I put it in drive it stops.