Agreed.

`99 Silverado 1500 and 2500 was the newer platform with the 4.8, 5.3, and 6.0 unless a 3500 which was your `99 Yukon'* close relative and could have had a 5.7 . Maybe that helps understand the cause . . . ?

Curious for the emissions process: What area do you live in?

Nice job indeed, and thanks for sharing!

The engine was the same, the computer was from probably a 2WD Silverado (engine, trans and rear axle swap.)

Georgia, more details below.

To further finish out this thread, I took it to a shop and had them run the Crankshaft Variation Learn Procedure (CKP) *. The new computer came with instructions from Alldata on how to do it.

Shop guy calls me in "This test wants me to blow up your engine!" We sat down in the truck and his scan tool said "Press brake, in neutral, hold gas pedal wide open"

I said "my writeup says run up to 4000 RPM.
We tried that and the scanner still said "waiting"
He then pressed the pedal to the floor, engine reved up an when it hit 4K, RPM'* dropped down and scanner said "done". (note, when it hits idle again, the tests ends so release pedal or it will over rev.)

Had him reset error codes, turn off and back on. Error was gone (would get flagged before as soon as started.)

Then drove well over 150 miles that week trying to get the drive cycle to complete. The Evap Test would just not finish. I have driven over 700 miles these last few months trying to get the cycles to complete. It finished in 20 miles on the new computer, but had the CKP learn error. Both computers got into a mode that the tests would never seem to finish. **

Buddy called me and he read in Ga: '96-'99 vehicles can have up to two drive cycle tests pending (later can have one.) Took it in to emissions, passed no problems.

Next week, it stumbled getting up the driveway and service engine light came on. Threw MAF voltage out of range. Cleaned contacts and was fine. Reset codes, no new errors but again, all drive cycle tests "Pending".

A few days lather after two short trips not even trying to follow the drive cycle, all tests completed. Go figure.

* None of my android apps could perform this step (Torque, DashCommand and others), nor could my buddies scan tools. We did later get a Snapon MT2500 that has the CKP Learn command.

** Found out later misfires will abort some of the drive cycle tests. I did replace the cap and wires and clean the plugs. Still #4 randomly showed misfires at idle. New plugs and no more misfires.