EZGO Goes Slow

[SwiftStrike]

We have a 2001 36v EZGO. It has the Fwd Rvrs lever below the seat. A couple of weeks ago I turned in the 9 year old Trojan batteries and bought new US1800 batteries and cables. It ran fine for a week or two, then the solenoid went out. Replaced the solenoid. Ran fine for another a week. Then the cart just started slowing down like the batteries were dead. Charged all the batteries, same problem. Checked all the batteries, over 6.3v on each, so they are charged.
Noticed that a couple of the cables going from the switch to the motor were getting pretty hot. Changed those cables. They still get warm but not as warm as before. The cart will accelerate just fine at first, but after about 100 yds it will slow to almost a crawl. I thought it may be overheating and shutting down, but I don't feel any excessive heat anywhere. It's not the brakes, because the brakes don't work. What should I be checking/testing next?

[SwiftStrike]

It is a 1999 TXT "Series" EZGo 36v

[cgtech]

OK, first, stop here. Fully charge the batteries, then check each battery individually. Post numbers here. Look for the "State Of Charge" chart so you know what's really up. If you don't have your meter set to give readings to the hundreds of a volt, you don't know their state of charge. You need a reading like 6.XX. One tenth of a volt can be the difference of 80% charged, or 65% charged. When you are actually putting a load on them it gets worse. Like 2 numbers after the decimal point. It makes a big difference. A 6v battery that reads 3v Does Not mean it is half empty (that battery would be effed).