Toyota Repair: overheating but heater blows cold, summit county colorado, alternator belt

Question
I have a '81 Toyota 4x4 longbed pick-up, 5 spd, 184k,22 R,  that overheats after about 30 minutes of moderate driving and aout 15 minutes of long climbs, like driving up Loveland Pass area of Summit County Colorado-9000 ft for most of the valleys.  The truck is carberated.  I put in a new thermostat, water pump, plugs, wires, d-cap, rotor, alternator belt, changed the oil and coolent.  A local shop recomended a new radiator after pressuring the system-no leaks!  What do you think? Other than the heater blowing cold air-no leaks, and the truck over heating it runs great.  Thank you very much!

Answer
I tend to agree with the shop that recommended replacing the radiator, it may be clogged and the heater core may also be clogged that's why there is no heat, try replacing the radiator and have the cooling system flushed this may clear up the heater core.