01 venture thermostat

has anyone had the pleasure of changing a t-stat, my van started to show me these symptoms:
no heat,
temp fluctuations(when rolling the temp gague lower than normal & when in stopped traffic the gague went higher than normal),
coolant is full,
top hose does not get hot, lower one does,
oil looks good.
am i diagnosing the problem correctly?
thanks in advance...

changed the stat, purged the air out and everything works great except the rear heat, is there a third air bleed for the rear lines?