1999 Grand Voyager transmission not shifting into high gear

Sticking valves. When is the last time you had the transmission serviced? Since it will shift when cold, I would suspect a valve body issue.

Dirty Shift Solenoids

Have to Google your trans unit or model
& see what the inside looks like, as far as
shift control items go

It may not be going into converter lock-up
either,that is some high rpm that will overheat it
also & ruin it for good

An expert at a shop ought to look at this---could be a shift module or electronic or mechanical problem.

It might also be a sign something bad is about to happen.

Electronic or mechanical issue?

Kinda sounds like it works when fluid is thick and not after it warms up. If it has been awhile since trans fluid and filter were changed it is the most simple thing to change. The torque converter is a big pump, it may be going and not providing enough pressure. This could be checked on most transmissions by a shop expert. Sometimes pressure can be adjusted externally.

The D inside of an O is for overdrive. It is an automatic overdrive transmission. There isn't an overdrive button on it. If you want to disable the overdrive you have to shift down a gear.

You have an internal pressure leak and will likely need a new tranny,sorry but you can take it to a transmission shop to confirm.

if you had 4:10 gears in the rear axle maybe. but i,d say your over drive is out. your truck should be running at about 2100 rpms or a little less at 70.

A common problem with most overdrive units.Overdrive should only be used above 40 mph. With the mileage odds are that you need to have transmission looked at professionally.It maybe time to consider rebuilding it.I do not see a trans service of being a benefit.

Your trans is stuck in safe mode, you are only using 2nd gear, this means it is not shifting but staying at a gear so you will not damage the trans. This is an electrical setting , however usually comes from the computer receiving bad information , rough shift, however it can be reset. Remove the positive battery cable for 30 minutes then see if it shifts, also check your fluid level, it can go into safe mode from low fluid if you made a turn and the trans slipped from low fluid . If your trans goes back into safe mode again have it checked, most important, do not drive over 45 mph or allow your rpms to raise over 3 , I have seen many motor problems that spawned from this type of trans problem, if not corrected.

Good Luck

U need a shopmanual..library sec629. Autotrans r so complex it may just b a bad connect etc. Get car scanned to show a datastream. It takes a factory tool..seek a privateshop