using new iPhone 4s on straight talk low signal strength

I am using a new I phone 4s on Straight Talk and I have only 1 to 2 bars maximum anywhere I go and then it will have no service at all.  Can anyone help?

I was a previous verizon customer and had 4 to 5 sitting in my home now I have 1 or 2 and if I walk around sometimes goes to no service at all.  Verizon did not have service everywhere I went but that was in hilly areas as I live in central Illinois and have talked to others with AT&T and they are getting better service than this as that is what towers Straight Talk uses.  I am getting a Gel bumper cover and have already tried the black tape it did not help.  It says I have 4 G sitting in house but cannot make a call and the 4G goes in and out also.

Thanks in advance

bigejohnson10@yahoo.com