1999 CC slower after new batterues

I have a 1999 CC 48 volt series (F-N-R) lever, when I bought it the previous owner had it running on four 12 volt marine batteries.

I put an All Sports lift kit, 22 in tires, repacked the bearing, changed the rear end oil, new factory cables, and 6 new 8 volt US batteries.

Now the cart is slower that than before, seems to run fine just slower, Oh and I ran it with the old batteries after I had put the lift kit on it.

Any idea why it is slower? Before it ran around 13-14 mph, now it is around 9-10 mph. and it lost some of its torque going uphill.

What can I check? or do I need a need motor? (ouch) don't really want to spend too much, its just a hunting buggy.

Any input will help

Thanks