My transmission is not shifting?

In drive on interstate at 60 mph after half hour or so transmission down shifts on a hill to third gear and then does not return to fourth gear.

Tranny trouble I washed my chevy blazer it locked into 4 low. Next day it came out of 4 low.I changed the filter now 3 gear revs, and drive the rpm are at 4 grand if you kick it it will rev then go into drive

I have a Blazer 97´with automatic transmission. Six month ago the transmission once passed to 2 shift it never came back to first even if the vehicle was fully stopped. After scanned the transmission with a Chevrolet scanner a solenoid 1-2 problem came out on the screen. I have replaced all the solenoids and after six month it started to fail again. I stopped using the car for about 3 weeks and started to used for other month without any fail for couple of weeks. What can be causing that problem? Is possible that there is a voltage supply problem? How can I check that? I will appreciate any support you can give me
Best regards

ABS light came on speedometer quit working and will not shift into third or fourth gear. Showed no signs of transmission failure.

It was the vss thank you.

From left to right, gear arrangement appears on dashboard as ordered:
Park
Reverse
Neutral
Overdrive
Drive
2nd
1st
She fires up without a hitch, smooth exchange from idle point, and purrs in reverse, but lacks follow thru on acceleration.
Instead of maintaining current speed by depressing the throttle, something disengaged.
Having to drop shift into 2nd around the 15 MPH marker for continued travel, and upshifting back to drive at a full stop, to be a two geared shit shifter when all I want is my automatic transmission back.

Why is my transmission not going into drive and high rpm.

Transmission didn't have 3 or 4th gear just sliped. After removing the 3-4 clutches and the the Piston. I found the clutches were burnt, but the seals were good. I cleaned the parts, checked the balls and installed the new seals and clutches. I didn't do any thing to the valve body. Where do I need to look for the reason whey the 3-4 still slip. And why is it only the 1995 tranny will work in the 1995 blaser. Junk yard say 1995 is all by it self and nothng newer or older will work.

Yes I replaced the filter. It goes into 3rd gear but slips. Reverse and 1& 2 gear are fine no sliping, clutcher were in good shape too. Band was also ok.

After giving you a donation, I have yet to receive an answer on why I still don't have 3 or 4 gear.

No I haven't had it scanned yet. Didn't want to drive it to far with this problem. What kind of scanner do I have to get to scan this. And do you plug it into the same port you use for the engine? Also like I said 1st 2nd and reverse work fine. Hopefully it is something in the valve body so I don't have to pull the tranny out again.