You have a lot of new parts. Obviously something is different from before. Old parts, it ran cool, fresh rebuild it runs hot. Clearly something has changed. As others have noted the fan really only affects low speed cooling. Since you say that the overheating only occurs after you've been on the road awhile I doubt that the fan is the problem. Head gasket seal SHOULDN'T be a problem, but a compression check can't hurt and besides it's a good idea to have a baseline on a fresh engine so that you have something to compare later checks to. Is there a spring in the lower radiator hose? If not, put one in. A new water pump shouldn't be a problem, but if all new parts were perfect there wouldn't be any need for warranties. The same goes for the thermostat. It's also possible as Feets noted that crud from the block could clog the new radiator. Did you have any head work done? It's unlikely, but still possible that if any work [ porting, hardened exhaust seats, milling, etc. ] was done that you now have exhaust gases getting into the cooling system. If you take a systematic approach sooner or later you will find the problem. Look at all the changes you made, since that is almost certainly where the problem lies. BTW you list S.Ill. for an address. That still covers a lot of territory, but if I can help in person or by phone PM me and I'll do what I can.