Toyota Repair: no heat or defrost but fan works 92 v6 pickup, head gasket, leak down test

Question
in the fall my truck overheated  a mile from home. i was out of fluid but had it checked out. one mechanic told me i should dump it, it was on its way out. my second opinion replaced the thermostat and water pump, and it seemed to be fine. now theres no heat/defrost. it was just a little low on fluid, but i think the engine sounds... tinny or not quite right. any suggestions. i will be taking it in but want to know what to expect and when i should really let it go. thanks.

Answer
Engine is pinging, or it's got a rod knocking & it's about to fly apart.
Warm the engine up & do a compression / leak-down test.
I'd almost bet money you blew a head gasket when you overheated it before & possibly roasted the #6 exhaust valve.

Record the results for each cylinder & get back with me.