Not shifting in to 5th Gear

I have an 08 Toyota Tacoma TRD Sport with an Auto Trans and while driving I have recently noticed that it is not shifting into 5th gear. This issue has been going on for the past week or so, but I have noticed that about 2 times out of 10 it will shift in the 5th gear. But more so it usually does not shift into 5th gear. It is causing more fuel to be used and I am afraid that there could be something going on with my trans. Has anyone seen or had this issue before, if so any suggestions to what it could be?

 

@gearcruncher

 

You have a computer controlled transmission .
Chances are there is a computer code tripping every time your transmission wont shift into 5th
First place to start is with a computer scan .
Any chance you have a scanner ?

 

Thanks gearcruncher, and no I don't have a computer scanner...

 

OK , no scanner . Auto Zone scans for free

 

I have the same intermittent (not) shifting to 5th gear. What data would I look for in the scanner . There is a lot of info, is there a code list or specific abbreviated code to look for? This is now happening with the new tranny installed June 2022. Would this indicate a computer glitch/problem? Thanks for your input!

 

Bring your truck back to the shop where you purchased the transmission . Its going to be very hard on gas until you get it fixed
How many codes do you have when you scan ?
https://www.tacomaworld.com/threads...th-pics-for-second-gen-4-liter-trucks.289913/

 

Only Scanner code is PO420 (Cat. Syst. Effic below thrshd Bank 1) ,but this does not seem to be related to A750 tranny.
I took it to install shop and they advised -NTF (they checked fuild level, test drove). It currently shifted correctly on the interstate drive home (6 miles).
Taco58