My transmission slips in drive but not overdrive why?

It is not going into neutral. Your overdrive band is fried on your transmission. Typical problem on these transmissions. Transmission will need to be completely disassembled to get to the overdrive band. Complete overhaul. Recommended when you read the owners manual to not drive these uphill for long periods of time without shifting to regular drive.

Hi Scott, The link below is a youtube video showing how to fix your transmition, I hope this helps......CHEERS''

Auto Transmission Problem
https://www.youtube.com/watch?v=WjNbeInU6-4

Fixing Transmission That Slips And Clunks

Either the transmission is shot completely or the filter is clogged and needs replacement and new fluid added

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_677dced97ad9bddf

my e40d goes to 2 then it wont shift it mack a winding noise and it wont pik up speed

Roger, that doesn't even make a whole lot of sense to me. If the overdrive is causing the transmission to slip, wouldn't it also cause the fuel mileage to go down? Are you sure the transmission is slipping? Or is the transmission simply shifting in and out of overdrive? If it is, is it shifting at the proper speeds? Driving at around 40 - 50 Mph will sometimes make the transmission go in and out of overdrive repeatedly. This can be perfectly normal.

Have you checked your transmission fluid level?

Is your overdrive off light flashing? If the transmission is actually slipping the OD OFF light should be blinking at you to let you know there is a transmission problem. Either that, or the Check Engine light will be coming on. In either of these cases, you need to scan your onboard computer network for possible fault codes.

it may be a bad transmission modulator valve located on the side of your transmission,vacum operated. a sudden downshift or forward shift when unexpected is sign of a bad modulator valve or a vacum leak to the transmission.best to shop around for a garage w/references when it comes to transmission work though. check all the vacum lines to your transmision,you need to look on the underneath side of your truck on the side of transmission for a loose or disconnected vacum line on the side of the transmission. when you feel the vacum line,follow it to the top of engine,the vacum line is about 3/8th line,and may be disconnected or losing air. to make this short,when you drive the car,start out in low gear and shift the transmission,manually from 1st to 2nd to 3rd does it do right with no slipping? if it does this right and shifts great manually,the modulator valve on the side of the transmissions bad,or a bad vacum leak in-between.thank you for choosing fixya.com

you have a cracked valve body. bleeding fluid pressure. the passage way where the fluid goes is the only differene when in o-d.

this seems like a problem of a loose belt inside your trans. if it hits overdrive and slips into nuetral till you lower the rpms then yea its a problem inside the trans.

well the low cost way to go first would be to try and change the trans fluids. If the problems still remains the it may be an internal problem