2000 V6 LS automatic

About a week ago, it seems that my fourth gear dissapeared. When I manually shift to the fourth gear, the car remains in fifth. Nothing else happens. What can I do to fix this or what is the cause of this problem. I'm schedule to do a PCM Reprogram on the 23rd. Hopefully this will fix some of the problems.

My car never reconized the 4th gear only becuase mine isn't a true select shift. After using it quite a bit it finally reconized it a couple times when I upshifted from 3rd to 4th. After I keep it in D5 or D4 it never reconized it anymore. If your's is the same as mine then it is D4 is usually useless, unless you are 0-140ing your car. That is why the switchover is so loose in the console. Once you are in those gears it is automatic. I have no idea about why mine never showed up untill later and why yours just left. I am just giving you my input.

Our problems seem very similar. But when I first got my LS, It worked on demand whether I was going 10mph or 80mph.

Does your's have SST? If not, this would be intresting if you get yours fixed, then I could have mind fixed. That is the least of my worrys though. I just want my transmission to work in general.