Well first forum have been too that no one tried to give some info. Are you getting a check engine light?
Sounds like iacv , maybe fuel filter . Iacv is on the throttle body back side looks like a big nut ..with wires.
Can take it out and clen . Do not touch the pintle on the end.
Check reference voltage at tps 5 volts also check the ground . Can check with key on also .65 volts at idle 4.50 volts at wot./wide open throttle.
What it sounds like vacuum leak. Not trying to be smart but a tb spacer is a waste ...your throttle plate maybe sticking on the spacer
Hence high...
Could be the cts/ coolant temp sensor located beside the thermostat housing , or vacuum leak , fuel filter .
Lean means not enough fuel. Could check fuel pressure 9 to 14 psi. 02 is working due to code lean.
Cts cost 10 bucks get it out of the equation . Hope this helps you Djk555
When going to closed loop ecm is sensing something is not right. Are you getting a service engine light?
If so scan it. Maybe cts/coolant temp sensor located beside the thermostat housing. May need to clean the maf sensor.
Maybe a vacuum leak . I could go on but will not ..take it to auto parts...
Sounds like it maybe in limp mode. Try disconnecting battery for 5 minutes or so.
See if you get gears back . If so watch out don,t drive over 50 may drop out again.
Is the speedo and or tach working good? Check fuses .
Maybe vss can check voltage on it . Jack rear of truck up use jack stands...