Poor FM reception
 

I decided to upgrade the sound system on my 1999 Blazer. I pulled the old cassette player and put in a moderately priced touch screen deck. The fm reception was crappy. It would waiver in and out sounding kind of muffled and back to clear reception. I thought perhaps the stock antenna wire was bad so I replaced the entire antenna and wire and that changed nothing. So then I assumed it was the budget stereo so I bought a better stereo and put it in and have the exact same issue. Anybody have any thoughts as to what is causing this?

Lack of a proper ground perhaps for the coax to the antenna?? That you replaced the antenna means you likely did not have a break in the antenna cable.

Have you tried to test the OEM radio to see if it also is having FM reception issues? If yes or no, the answer might help point to the problem.

Stock stereo work fine

So the original radio works with the new antenna?

Yes it does but I have tried 3 aftermarket stereos and they all have the same reception issue

That is nuts. It has been awhile since I installed an aftermarket radio but one of the things I would think would not change is the connections to the antenna! Does the plug and receptacle for the new radios look the same as for the OEM?