I was just driving home doing about 65 and the automatic trans kept wanting to downshift. After letting off the gas for a second it would upshift for awhile and then repeat the problem. The fluid level is not low, dirty or burnt and was replaced about 9 months ago.

SOURCE: Sierra 3500HD rough idle

do a good tune up it is not the tranny . you might think about a good diagnostic test to make sure it is not a senser it is hard to say for me onless i could look the truck over my self . good luck

SOURCE: Hi, I have a 1998 Chevy 3/4 ton 4x4, automatic

This is directed to the secound part of your question.I don't know much about transmissions but i'am sure someone on this site does. Might want to look on the back side of intake to see if there is any signs of the intake gasget leaking. The only other place it could come from is a freeze plug or head gasget but i have never known them to leak from there but its posible. If you got a puddle right under the hole on the inspection cover for flywheel witch is red in color it would be the front pump seal in trans.

Harvey N Tawatao

• 3854 Answers
• Posted on Apr 25, 2009

SOURCE: 99 jimmy trans issue have fwd & rev but....

Best thing to do is get the ECM on the jimmy scaned for codes. I believe Auto Zone will scan for free and some transmission shop as long as there honest will scan the ECM too and let you know what you realy need.

The ECM controls the transmission and if there is any conflicts between the transmission or engine the Jimmy will go on a limp mode and your transmission will not shift to OD and may seam to be slipping.

If it is a transmission problem the scan will pick it up, same as to if it's a engine problem.

Good luck and hope this helps, Just trying to save you some money by finding out what is causing the problem.

SOURCE: 99 jimmy 4wd sl trans issue have fwd & rev but....

It sounds like your describing your torque converter and that its staying unlocked. you might want to check your brake light switch/s if they are malfunctioning it could cause your problem. Also possible that your fuel filter and/or CAT might be clogged.

Bruce Bracey

• 1000 Answers
• Posted on May 03, 2009

SOURCE: at times the transmission bangs a little hard from 1st into 2nd -

If the truck is shifting properly and does not feel like it is slipping, you are ok for the time being.

I would however suggest draining the fluid in the pan (roughly 4 qts.) and replacing it with fresh fluid.
Run the truck for 500 to 800 miles then do a complete fluid exchange and filter.

The reason I suggest this is, you do not want to "shock" the transmission. Transmission oil never really wears out but the additives, cleaners and conditioners do. By replacing only 4 qts you can slowly introduce the conditioning properties back into the transmission. If you were to change the oil all at once you may delaminate clutch material and cause a transmission failure. I'm not trying to scare you and the chances of ruining the transmission are remote, but if you are not aware of the vehicle history it is better to be on the safe side.

I hope this helps, let me know. Good luck.
Regards,