96 48v series cart running slow

[midtown15]

i have a 96 48v series cart that is getting the best of me. it will only run 8mph on flat ground. it will climb a hill, just at a very very slow speed. i installed new trojan batteries along with 4 gauge wires. i get the growling noise from the rearend that i've experienced on other carts due to bad batteries not getting enough power to the motor. i'm not sure that i'm getting the proper voltage to the motor. i've checked several things to make sure they are working, but it doesn't have anything that is completely broken, just something not working at it's full level. any help would be greatly appreciated!