36V Western model 400 running slow

[Bmekar]

I just purchased a 1997 model 400 and have taken it out golfing a couple of times. The last time out my buddy had to get out a couple of times and push up the hill and at the end of 18 it really couldn't make it up the drive on trailer. The batteries all have a date code of May 15 on Trojan T105's. Each battery tested at 6.39V fully charged and the pack read 38.6V. I put my DVM across the pack and started driving. The voltage immediately dropped down to 33-34 volts and never rebounded back up toward 38V. Instead the voltage remained hovering around 34V. I only ran it for a couple of minutes but am sure that the voltage wasn't going to get any better. I am not sure if it is the batteries or controller. Can someone please point me in the right direction?