I have done 40,000 mile transmission fluid and filter changes, am now at 175,000 miles on 2001 2WD Blazer with 4L60E transmission. Recently switched out 4 regular quarts to Castrol High Mileage Dexron III-compatible fluid just for good measure and went on a 350 mile round trip. Just before heading back, noticed dipstick had dislodged and blew about 1/2 cup of transmission fluid onto the engine. Washed down, and wrapped dipstick top seal with one wrap of electrical tape to make it seal much tighter. 50 miles later at 74 mph, noticed my normal 2100 rpm had increased to 2400 rpm. Went back to normal for 100 miles after stopping for gas.

Made it home but problems increased over next 2 days (needing higher RPM's to shift). Had another 1/2 cup of transmission fluid leak out, but not from the dipstick this time; couldn't tell where from. Changed transmission fluid twice using regular Dexron III by siphoning very slowly through dipstick - no improvement. Second morning, went on a short trip and suddenly almost no movement in any gear. Roared 1/2 mile to get home. Then could only inch forward (D 3 2 or 1) or backward in driveway if revving above 3000 rpm.

Thought about/researched for a week, and with little hope finally dropped pan and found transmission filter was lying in pan. I put in a new seal and filter and noticed I could not push filter up very far. Found filter blocked by a wire tray out of place instead of tucked under a plate! I had changed a shift solenoid about 12 months prior (cracked the old one changing the filter seal at that time) and probably left wires out of place. Tucked wires into their proper place and could push new filter in farther! I think seal swell additives in the high mileage fluid changed the grip of the transmission seal and/or finished pushing the "old" filter almost all the way out so that I started sucking air. After a properly seated filter and a refill, transmission worked again seemingly normal. I wondered if I might have done some damage so added 24 ounces Lucas Stop Slip which supposedly builds up a protective coating over time on clutch surfaces, and restricted myself to shorter trips the next two weeks. So far so good. Hoping this helps someone, and would like to hear comments if anyone has done OK after a similar situation.

 

Time will tell. Usually running trans without fluid cooks them pretty quickly.

 

6 month update - still running well and have been on many long trips. Guess I got just enough fluid flow through fallen filter to avoid the worst.