no 4g on rooted droid bionic

i have a motorol droid bionic that's a 4g lte capable phone. it operated on the verizon network for 2 years with no issues using alternate roms. since i've switched it to straight talk and i use a different rom other than the verizon stock rom i do not get any 4g connectivity. as soon as i switch to the stock verizon rom i do, i used verizons service for 2 years with no issues using whatever rom i wanted on my phone my network connectivity was always the same.. any help regarding this would be greatly appreciated, thank you.