yes this is the same truck as in my signature. im pretty sure the thermostat is working good. it heats up and cool down normally. i also checked the egr as mentioned earlier in a post. it seemed to be working fine. i just changed the head last week with one that had been rebuilt from a dealer. but it was doing this same thing before i changed the head.

1986 toyota pickup rte 4wd sr5 xtracab---bone stock