Need Advice-battery issue?

[bthomas]

I have a 2005 Ezgo TXT series cart. The cart specs are listed below with performance after install. I just tested the batteries and I am concerned that they might be an issue. Can you advise me on your thoughts about these batteries? I had planned on converting to a 48V system when I needed new batteries, so is that time near?

December 2005 Trojan T-105 batteries, 36V
Plum Quick High Torque motor
Curtis 400V controller (factory installed)
Complete 4 gauge wiring set
23x10x12 Alltrails
Performance:
flat= 22mph (fine)
hills= 10-12mph (slight improvement over high speed motor)
Battery Readings:
6.21/6.24/6.25/6.31/6.28/6.28, main=37.6

When you convert to 48V, is there a difference in performance between 6-8V batteries and 8-6V batteries?