with that drivetrain you should be able to pull the weight you listed fine...without issue. If you are leaking transmission fluid and overheating those may be just lack of maintenance and the age of the truck in question. Likely whomever owned the truck before never towed? OF course towing stresses the cooling etc. Given the age of the truck I would install a HD radiator if available and then apparently you'll have to address the transmission issue. I don't know specifics for what that vehicle is rated for in weight...but I certainly know its capable of pulling that type of weight without a problem...I drove a few 99-2000 one ton for many miles with same drivetrain...
