Transmition overheating under load - 1995 Isuzu Trooper

manual transmission
indicates counter shaft bearing or clutch shaft input bearing failing
reasoning is that for those gears the load is transmitted across to the counter shaft placing a side load on the bearings while 4 gear ( not really a gear ratio) is direct connection from input shaft to out put shaft and removes the load from those bearings
the noise is actually from the gears coming slightly off the proper pitch contact of the teeth from the bearings failing

there are several problem that will give this indication and your information is not comprehensive enough to make a good diagnosis
the time factor is critical as some time could be 5 minutes to 5 hours and driving is too loose as it could be at highway speeds or stop go traffic , hill work or under load
so I will give to certain conditions that will over heat the car or cause a rise in operating temperature
head gasket--check with compression test
low water level-- check at cap
faulty radiator cap--have tested
partially blocked radiator--have a flow test done
fins on cores falling off --replace radiator
overheating transmission oil--check the transmission is fully operational as high speed with out over drive in will cause a rise in temp
if in traffic --check viscous fan and fan operation if electric
if under load -check load and tyre pressures
check for brake operation- adjust hand brake to full off
run the fault codes to check air/fuel ratios and timing
check for failed cat converter-- blocked exhaust system

check alternator output under load

Heater core may be partially plugged. Also check the heater control valve to see if it's letting water into the heater core.

How do you know that your transmission is overheating? Do you have a heat gauge for it? Does it stop working? Won't pull under load? You need to give more information than "transmission overheating"

check thermostat

You have a serious problem in the transmission that is causing allot of friction, what this is will require the transmission be torn down and inspected. Get the factory representative involved in this is the dealer isn't doing there job.

have auto zone run a scan on the truck its free overheating you need a seperate cooler for you trans pulling trailer put a high load on trans this will make the trans last longer and run cooler I would put the cooler as low as possible in the very front of your radiators

either the ECM (engine computer) or the relays. There is a set of relays just under the glove compartment in these jeeps. The relays in there control the door locks, security system, rear defroster, and power antenna

It is a relay or a circuit breaker that is overheating.