James - I appreciate your response. I'll start by saying there is no problem with reverse.
As far as the forward gears, the problem is not exactly the same every time. When I drove it a couple of weeks ago, the issue was upshifting from 2-3. It also had delayed upshift.
After receiving your message, I drove it today for the first time in several weeks. When cold, it was having a delayed upshift initially, but after a mile or so, it seemed to upshift fine. It also was shifting 2-3 fine, but didn't appear to shift from 2-1 or 1-2. Evening after stopping, placing in park and then back in D, it seems to be starting in 2.
I don't have any experience with transmissions and don't have the knowledge to check the internals. I was really just wondering why I started having problems after the fluid (and subsequent modulator) change given I never had any issues in the prior 15+ years and several fluid changes. Just trying to figure out the best path forward.
Hi, you have provided a ton of info in this post.
The next question will be: How does it drive in "L"? When you manually shift to "2" does it give a firm upshift, or is it squishy?
Do you get a firm buckle up when you go from N to D? Feel the same as going from N to R?
Assuming that you didn't do anything inside the valve body...The fact that Reverse is good, and you are getting a delayed buckle up in D tells me that you are taking too long to accumulate pressure. This is typically from a leak that is bleeding off "some" of the available line pressure. As the transmission warms up, the fluid flows easier, which causes the leak to get bigger, but the pump gets more efficient, and flows more fluid. That just means that your leak is "just right." Unfortunately, it also means that you have a leak. And you gotta fix it before it starts to slip. So you are due for a hook-ring, seal, and gasket replacement. It is possible that your valve body has a stuck spool valve, but I doubt it. Either way, a pressure check will tell you. Most likely the forward clutch outer piston seal.
Fix the leak, and then the pressure accumulators will function again. Then it will shift properly again. Of course it's convenient to rebuild the transmission, and replace all of the seals while it's open...since they have all seen the same service interval.
If you have a compressor and a rubber tipped blow gun, you can pressure test a C4 in the truck. 100 psi will do it. then you'll know for sure.
