When you're in the truck, and you pull the selector into gear, you should be able to feel the trans go into gear within a second or so. Any longer would indicate a problem beginning. The easiest way to replace the fluid would be to get it to a garage that offers transmission flushes. This will replace all the fluid in the system. It can be done at home, but it's kind of a pain. you'd have to undo the line returning fluid to the trans and let it drain into something that would hold about 3 gallons of fluid, while you're pouring new fluid into the fill tube. And you'd need someone in the truck to hold their foot on the brake with the truck in gear, to activate the trans pump.
First off do it your self cause otherwise that means your gonna drive to a shop unless you have it towed.
Second there is no brake activated pump in these transmissions!
Its actually quite easy to do flush at home a helper is of great help though.
From what I can find the lower cooler line from the transmission is your Pressurized line going out from the tranny to the cooler.
So remove the top line from the radiator which is the return line to the tranny(make sure the line you remove from the rad is the top line at the transmission). attach a piece of hose onto a spare short piece of line or the appropriate fitting to install in your rad where the return to tranny line goes, and run it into a bucket(preferably white) Remove the transmission pan, install new filter, clean and reinstall the pan with new gasket and torque the transmission bolts to 13ft lbs. refill tranny with 4 qts of fluid.
Get a funnel that will fit nicely into your transmission fill tube and secure it so that it will stay with out having to hold it. I used electrical tape and wrapped it around both so it wouldn't move.
Now with the vehicle in neutral and the wheels chocked. Have another 6 qts of transmission fluid ready, its a lot easier to use 1 qt bottles.
In neutral have your assistant start the vehicle, and watch the bucket to see the transmission fluid coming out of the return line into the bucket. As the fluid is pumped into the bucket simply add the same amount into the fill tube with your 1 qt bottles. Continue to do this until the fluid coming out of the return line is clean red. Then have your helper shut off the vehicle.
Simply reinstall the cooler line and ensure that the transmission is at the correct fluid level in park while idling.
So you have filled the transmission with new fluid and filter this will be sucked up and pushed through the transmission and through the pressure line to the rad and will be pushed through the rad and out through your rigged up line into a bucket. there by pushing new fluid through pretty much the entire system of your transmission.
This is exactly what you will receive at the speedy lube shop. but a whole lot cheaper.
The trick is to keep adding fluid as the transmission is sucking it out of the pan so that it does not run dry as you are exiting the return line into a bucket instead of allowing it to return to the transmission like it normally would.
It is how ever pointless to do this until changing out your rad if your radiator is the source of the problem.
things you need to know about flushing your trans... NEVER get a pressurised reverse flush... it washes all the stuff from the filter and clutch packs and any worn parts back where you really don't want them(though out the entire system) thus reason why the trans will fail in short order.ask me how I know... . 2.) Trans flushing can be done at home
