Here's my problem I posted on another site. They have a good "beginners list" of things to describe to help everyone diagnose the issue.

1. State model, year of vehicle and mileage: 2001 GMC 3500 DRW 6.0 gas 230,000 miles

2. How long did you own the truck? Recent purchase? Brought it home Friday and noticed transmission fluid on the ground the next morning.

3. Any service engine light: yes/no. Intermittant check engine light?
This is called CEL or MIL Yes, intermittent

4. Fluid level okay with the engine and transmission warm? Check on
a level surface? Fluid level is good. Was topped off before I brought it home and checked before the couple of times I've driven it since. (leak is not bad enough to have to add any fluid in the 150 miles I've driven it so far)

5. Have you retrieved Codes? AKA DTCs Diagnostic Trouble codes.
Fuse was blown so OBD2 port didn't work before I dropped it off at the dealer

6. Fluid color and smell? Red or Brown does the fluid smell burnt?
Did not smell burnt and was red (probably still good since the "top off"

7. Speedometer reading correctly at the appropriate speed? Are the tires the within OEM specifications and size? Use your GPS and verify speed. electronic transmissions remember?
Speedo works and speed is GPS verified

8. Is the transmission shifting normal? Is it shifting hard? Do recall the shifting symptoms or any shifting changes before or after the check engine light or after you retrieved codes.
Shifts through the gears just fine, holds overdrive fine and downshifts fine. Goes into reverse fine. PROBLEM: when at speeds above 45mph or so when decelerating (like when coming into a town or getting off of an off ramp) the rpms hold around 1500 rpm for a couple seconds then drop to 500 rpm and a loud winding sound ("Loud" being loud enough to hear it over the radio which is loud enough to drown out the dual exhaust the previous owner installed). It does it every time slowing down from those speeds. I can get it to stop if I hold down slightly on the accelerator to raise the rpm's up to or above 900 rpm while using the brakes to slow the truck down (I'm not driving the truck until I get this fixed because of this "solution")
9. Did you or anyone else conduct any kind of maintenance to the vehicle recently? Just fluids topped off and engine oil changed and new shocks all around.

10. Can you explain the type of driving? Heavy towing? Snowplowing? Truck is a welding rig. Has about 3000 pounds on it all the time (welding bed, small amount of tools and Lincoln pipeliner)

11. Typical weather. Arizona hot mild winters? Minnessota cold. Please explain. Southern Illinois. Been a long cold winter here got down to -30 wind chill a couple times but average 20-30F mild to hot summers. Truck goes anywhere in the United States

10. Any problems with driver commanded/selected shifting into any gear?
ie.. 1st, 2nd, 3rd, 4th, Rev?
No, shifts into any gear just fine

8. Describe symptoms: Does the transmission refuse to shift in first? Will it shift into second and just stay in second gear?
Explained above

8a. TCC Locking? Is the transmission slipping in any gear?
Do not believe so. Truck will not be towing anything

8b. Is the transmission shifting into all FWD gears? At the
normal RPMs while the shift selector is in drive? Is it shifting later
than usual?
Seems to be shifting at the correct rpm and time

Can your vehicle shift into all gears?
Yes

 

Any ideas at all?!?!?!?

 

Try starting over. Your thread is difficult to read.

From what I gather you have a small leak that has you concerned.

If that's the case, where is it coming from? front or back of trans?

Without being able to look at it, I would guess its most likely a seal.