99' transmission slipping?

While driving today, the van started hesitating and just stopped moving. Turned to engine off - then restarted it - it would only go around 10 mph. (The daughter was driving & I was nowhere around, so I am going by her story)
My brother-in-law checked the transmission fluid and noticed that it was very low, so he added some fluid. Now all of the gears are out.
I am having the van towed home and I will make sure he did not put too much fluid.

If it is not the fluid - what else can I check?

Is there really something in the transmission the can be tightened to fix slippage?

Well - I had the van towed to a transmission shop. When I find out what went wrong, I will post it here for others to possibly learn from.

Sorry to say - the transmission is scrap. I can not afford the $1500 to replace it, so the van is going back to where we were buying it from. JDByrider sells nothing but sh!t anyways.

Sounds like you found out just in time the tranny was bad. You can get a used transmission for about $700 and put it in yourself, but if its not your car yet, find another one.