Combination of Error Codes

Any ideas about what may be going on here? Thanks for any help!

2001 Toyota Tacoma 4WD, 4cyl 2.7L, 110 K miles

The check engine light came on -- codes were P0125 and P1135. I reset the light by disconnecting the battery cable and drove a couple of miles. When the light came back on, a new code appeared P0171, the other codes did not come back up.

The following was done:
1. Removed and replaced spark plugs
2. Cleaned the MAF sensor
3. Replaced the air filter
4. Reset the light

Then I drove the truck, the light came back on, one code: P0125

1. Replaced the thermostat (actually looked fine)
2. Replaced the ECT sensor (could that have been in a tougher place to get to?)
3. Refilled the coolant
4. Reset the light

Then drove the truck -- the light came back on, this time only P0171.

1. Checked for coolant leaks
2. Found that I had knocked the vacuum line off from the air intake, reconnected it.
3. Reset the light

Drove the truck, light came back on. This time all three codes came up: P0125, P1135, P0171.

Any suggestions for the next step?

 

I suspected that's what it would take -- thanks!! That will be my next step.