I've been fiddling with the stock carb a good bit and recently I decided to drill out the primary jet a few sizes as my wideband showed it was running 16:1 or higher during cruise. Now the cruise afr is down to about 15:1 but if I try setting the idle lower than about 950 or so it goes full lean and dies. I didn't have the issue until I resized the jet. I tried to clean all the passages with carb cleaner but it didn't seem to help at all.

 

Toyota only used one or two jet sizes and let the design of the carburetor compensate for altitude.

Is the fuel level in the middle of the sight glass when the truck is in level ground?

Have you checked for vacuum leaks? Exhaust leaks?

It may also be time for a carburetor rebuild to get any gunk out of the various passages and re-seal everything.

 

Well I rebuilt it maybe 3 months ago. Float level is good fuel filters are all replaced and I've spend the last 2 weeks getting all the exhaust leaks and vacuum leaks fixed. I'll check tomorrow and see if maybe another vacuum leak has popped up.