Transmission issues I'm fairly sure the tranny is gone, but here's what's going on: My wife was driving at highway speed yesterday when she heard a big "clunk" which shook the van. The van then lost drive and coasted to a stop. She had absolutely no movement in any gear. The van would go into park. After letting the vehicle sit for a moment, she started had all forward gears, but no reverse. However, you could only go about 5-10 mph before you would lose 1st gear and have no movement in any gear again. I pulled the codes and this is what I found: P0720, 0734, P0732, P0700. They're all transmission related, just wondering if anyone with much more knowledge than me has any imput. Am I looking a a new transmission or could is possibly be a sensor or solenoid of some sort. There is no grinding when in any gear. Any help would be greatly appreciated.

i have never heard of putting atf in a manual gearbox,i'm sure its 90 gearoil

You should not use overdrive unless you are steadily going highway speeds. I had one of those and my ex liked to use cruise control on windy coastal roads. This caused it to shift back and forth from 3rd to overdrive constantly. So I disconnected the cruise control so he couldn't use it. Lol. I'm not suggesting this for you. You should keep overdrive off for now and have your transmission serviced. New filter & oil & flush the cooler. Make sure you ONLY USE THE RECOMMENDED FLUIDS!!!!!!!!!! See if that helps. Do not use overdrive pulling a trailer and going up a hill and do not use it if you are on windy roads where you are slowing down alot of times. Try letting off the gas for a second when you do want to engage the overdrive. Remember to always check your automatic tranny fluid with the engine running and fully warmed up.

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sound like the trans is gettin hot, i would have a trans cooler installed

make sure the fluid is clean and topped up , the slipping in and out of gear at highway speeds indicate internal problems inside the transmission not the slave or master , those just release the pressure holding the disc to the flywheel . my guess is it has to be internal damage with blocker rings slipping maybe from dirty oil or heat damage.put a drop of trans oil on white paper and check for dirt or smell it for signs of being burnt.

Well every gear has its limitations. I am not sure what the mph ranges for each gear are, but i've gotten to 60+ mph in 3rd gear. The only thing about driving on the freeway in 3rd gear is that it is alot less efficient mileage wise. Your turning more RPMS while on the freeway in 3rd gear so you burn up alot more gas.
Driving in D3 is driving in 3rd gear. It could burn up the tranny but it depends on the vehicle itself. It is not really made to do highways speeds in 3rd gear. It should be in 4th or 5th (OD)

check the oil strainer

I had the same problem but eventually lost reverse. Had to get a new transmission... $2,300.00

Sounds like you may have a worn out CV joint and the clicking may stop with an oil change. Good Luck

your highway acceleration problem could be a coil problem. Not sure if that year of chev has coil packs or not but experienced same thing with ford 5.4L. went through 3 coil packs and did the same thing each time before biting the dust. Transmission seems to be sticking on the 1to2 upshift and could be a sticking solenoid in the valve body of the tranny. If the shifting problem persists then the tranny deffinately has to be rebuilt. It's made it quite far if tha is the original tranny, you cant expect too much life out of it if it has been worked hard. I highly doubt a fluid change would help at all. Or if you want, you can buy a can of new truck from GM for about 25 to 35 thousand bucks! Typically works great!

is ''s'' light blinking on the dash
the tranny uses a speed sensor mounted on the outer side,
this sensor calculates the transmission speed and compairs it
with the vehicle speed if the tranny speed sensor is not working
proper this can cause the miss shift