I need to know a little about the trans.
1. Do you know which trans you have?
2. If you do not know which one you have can you tell me what the pan looks like?
3. Can you tell me what happened before the trans stopped pulling forward?
Is the check engine light on with the engine running?
With all you have told me I would have to say That your problem is going to be one of three things,
1. A bad shift solenoid
2. A stuck valve in the valve body.
3. The gear selector switch is bad.
The only one of the three that i can help you check would be the gear selector switch.
Does the truck pull if you put the shifter all the way down in manual 1st gear or second? If it does then replace the gear selector switch mounted on the drivers side of the trans on the gear selector lever. If the truck does not move in manual 1st or 2nd, then you will need to take it to a trans shop to have them do a diagnostic on the trans and shift solenoid block.