On idles and on Gas mileage being better.

The automatic transmission 22re requires an 850 RPM idle. The EFI trucks surge if the idle is too high, but 850 is not a problem.

I would suggest that people experience better mileage only because they have fixed a worn out top end (possibly bottoms too) and are experiencing what the vehicles got when they were new. My 89 auto with all the sensors working and in tune can get (and has) 23 at 70 mph of I am not driving into the wind. These trucks were made when the speed limit was 55, so its not surprising that they get the highway speeds written on the EPA listing when you drive 60MPH.