I have problem in final gear (lookup shift gear )when it should go to lookup gear it's back to 3th gear ...can any one have any answer?

I used to have an old Holden that did that. On the side of the gearbox were 2 levers that changed between gears. Sometimes if I was a bit quick on changing gears , it used to lock into 1st and reverse at the same time. By using a shifter spanner, I would crawl under the car and manually move 1 gearlever at a time until they clicked into the correct position. You may have the same problem where the gearbox has stuck in 2 gears. Have a play with the shifters while someone moves the gearlever to see if it will drop back into its correct position.

Time to have transmission overhauled. Call James at 1-972-467-3702 in Midlotheon Texas if it's handy. Does great work at his shop.

cut the blocking section

Do you have a warranty?If so take it back,it may have a recall.

Possible slave cylinder or clutch needs bleeding

Gear lock in tranny or bleed clutch

auto tranys look somewhat like a jet engine with blades that a pushed by trany fluid. In 3rd or fourth gear these BANDS are damaged. looks like a trany overhaul.

your tranny is going into limp mode,
the computer is not seeing info from the speed sensor,or output sensor,or the input sensor.
if you have the van checked for codes it will tell you which one,none are too expensive

by the sound of this problem it seems to be 1 of 2 things it could be a bush or your gear shift cable needs to be adjusted

I know you don't want to hear this but theis transmission has failed, the clutch pack for gears 3&4 has failed, the trans will need an opverhaul.