5.9 01 1500 4x4 transmission suddenly won't go into great
 

My trucks been running great, until today. Coming home it suddenly felt like my breaks were catching when I went to take off at a stop light. Got home ok. Went to take my sister in law to work and it did it again, pulled into the gas station and suddenly wouldn't move. Shut it off restarted the engine and would move a couple feet. Did this a couple times to get it parked out of the way. I had all my fluids changed when I purchased the truck few weeks ago. Just got gas yesterday night. Checked fluids everything's good, climb underneath and nothing leaking or out of place I can see. Went to get the truck and bring it home tonight and it wouldn't move. Need help before I have sell my betty.

I'd do a pressure test on it, Could be the check valve is clogged/stuck.

Drop the pan, see if anything interesting is in there.