For those that are suffering from insufficient heat in your Gen1 (or even later!) Dakotas, here's two hints I found.

1) 195F thermostat. Really. Don't even THINK about a 180 or $DEITY forbid a 160.

2) Reverse flush the heater core.

On my stepson's 1988 3.9L, I disconnected the return hose from the intake and the heater hose from the water pump, put a 5/8" female hose fitting on the hose from the water pump, connected it to city water (nominally most places about 30 PSI, the leak test says to pressurize to 45PSI ... if it blows, it was already a goner!), and ... after a few gurgles, it spat out the nastiest looking brown crud and ran brownish for about ten minutes before it was completely clear coming out.

Now, I have heat.

Along with the thermostat - dunno if it was a previous owner, or if it came from the factory this way, but the stepson SWEARS he put the last thermostat in the way the previous one came out - upside down (!!). They do heat up better when the thermostat is turned the correct way.

RwP