you need the fast idle adjusted on the engine you may have idle set where it sounds fine in idle but not high enuff when dropped in gear.
a pile of poo
Check the motor mounts.
vacuum leak?
autozone will scan codes for free.to see what is wrong!!
Could be a very dirty fuel filter.
MAF senso, or transmission fluid.
either bad gasket under throttle body or bad iac valve
I have 91 chevy k1500, It does this, Sometimes it will idle a few minutes, then jump to high idle and check engine light comes on, And sometimes its as soon as i start the engine... I was told it was a vacum leak, But im no mechanic
Bad oxygen sensor
Either you were low on gas, you need a transmission check, or the fuel pump may be going out.
Sounds like a vacum leak to me.