Sounds typical to me. Time for A/C Mod. Below is from Baz's tips.
It will stop the flow of hot water through the heater core when the AC controlls are in the MAX setting and the OFF position providing cooler temps and preventing the hot pocket of air down by you feet. I went to NAPA and asked for the 'hot water shut off valve' from a 1990 Ford Ranger with a 4.0 V-6, I also got 4 - 5/8 hose clamps, a couple feet of 1/8" vaccume line a a 1/8" plastic "T" for the vaccume line. To begin the install loosen the cap on the radiator overfill to remove pressure from the system (do this while the engine is cool). On the passenger side of the engine compartment there are 2 - 5/8" hoses that come from the firewall and continue to the engine, these are the heater hoses. Cut the hose closest to the drivers side (It does'nt really matter where, I did mine about 6 inches after the fire wall). Then holding the 'shut off valve' with the vaccume controller twards the pass side install the portion of the heater hose coming from the cab to the top left nipple on the 'shut off valve'. Tighten the clamp. Install the portion of the heater hose coming from the engine to the top right nipple and tighten the clamp. Next cut the heater hose closest to the pass side in the same location as the previous. Install the portion coming from the cab on the lower left nipple, tighten the clamp. Now install the portion going to the engine on the lower right and tighten the clamp. Measure out how much of the 1/8" vaccume line you need to reach from the bottom of the vaccume canister on the shut off valve to the white vaccume line on the pass side that goes to the vaccume operated door underneath the pass side cowl. Cut that white vaccume line and splice in the 1/8" plastic "T". Then run the 1/8" vaccume line you meassured out from that plastic "T" to the nipple on the bottom of the vaccume canister on the shut off valve. It sounds more complicated than it is. Once you do it it will seem real simple. Happy trucking!
Thanks Bryan Central Texan