2000 Sonoma Temp won't get past 150??

[C Mouse]

I just bought a sweet 2000 Sonoma!! Very nice but the temp won't get past 150 so there isn't any heat.
I replaced the thermostat and no change.
I hear the intake gasket may be bad but that just seems odd.
Any ideas?
Thanks in advance,
Mouse

 

[fishin_wi]

kinda late i know, but fan clutch staying on possibly?