This is a guide to changing the fluid on the New Venture Gear 3500 series 5 speed transmissions found in GM Half Ton trucks. Required Tools & Materials 17mm Allen Wrench or Socket, preferably 1/2" drive - my local parts store had it in stock Socket Wrench Torque Wrench (ft/lbs or Nm) Oil/Fluid Drain Pan Rags Thread Tape Funnel 4ft of hose 3 Quarts of GM Synchromesh Fluid #88900333 - Summit and Amazon both carry the fluid, just search that number and the AC Delco bottle will come up Procedure: First, if you need to raise your truck on jackstands, make sure the vehicle is as level as possible. Also, make sure the vehicle is STABLE before crawling underneath. I am not responsible for any stupidity on your part. Next, I checked the fill plug to make sure it came loose. No sense in trying to drain your fluid if the fill plug is stuck, then you have no way of filling the transmission. Using your 17mm socket, loosen the fill plug, located on the passenger side of the transmission, just in front of the Y pipe. It is the top plug in the following picture Have your drain pan ready, as fluid may come out of the fill plug hole! Then, with the fill plug out, proceed to the drain plug, which is the lower plug in the above picture. Loosen the drain plug and again, have your drain pan ready. The fluid comes out pretty quick, so make sure you have rags handy, it gets everywhere. Here's the transmission with both plugs out Here's what the drain plug probably looks like once you pull it out Filings are to be expected. Chunks are not. If you have chunks of metal and debris attached to the drain plug or in the drain pan, chances are you have some sort of internal damage. Consult a transmission shop before going further. Once you clean the filings from the drain plug, clean the threads. My drain plug had remnants of old thread tape on it. I cleaned mine and applied new thread tape. Reinstall the drain plug into the transmission. Torque to 15 ft/lbs or 20 Nm. I used a clear hose and a funnel along with a helper to fill the transmission with new fluid. Insert one end of the hose into the fill hole. Have yourself or another person pour the GM Synchromesh fluid into the funnel. Repeat with the second quart of fluid. Once you get to the third quart, pour the fluid until it begins to spill out of the fill hole. The actual capacity is 2.2 quarts for those who need to know. Once it spills out, insert the fill plug and torque to 15ft/lbs or 20 Nm. You are now done changing the transmission fluid on your NV3500. Drive the vehicle a few miles and then check for any leaks and then retorque the plugs.