My
1. did they bother to tell you what the original CEL was? If it was P0110 that doesn't relate to the MAF (mass air flow) sensor, I don't think, rather the FSM says it relates to the air temperature/boost pressure sensor otherwise known as the MAP sensor. If I'm wrong and it does relate to to the MAF sensor the first thing to check is wiring continuity and if the wiring is plugged in solidly as if bad both can throw a code and the MAF wiring/plug are known issue points. If I'm right and it's the MAP you can pull it yourself (4mm allen key if I recall; don't drop the tiny washer) and clean it or just replace with a GM PN 55206797 which costs like $25 and see what happens.
2. I assume by EGL you mean EGR which has, as far as I know, little or nothing to do with the issue at hand and is virtually the first part a clueless dealer will toss on your vehicle to see if it fixes something (surprise if it doesn't you still pay for the new part) notwithstanding the fact that it can be cleaned and put back on or cured by a GDE tune.
3. to be blunt if they say and charged you for cleaning the intake valves and adjusting the timing they flat out LIED as the only way to clean the valves involves pulling the serp belt, timing belt, cams, valve cover, head, etc plus the only way to "adjust" the timing is to do a timing belt job so unless they charged you like $2,000 they did neither of these things. To the extent the electrical timing (not to be confused with the mechanical timing of crank and cams) is "adjustable" that's programmed into the ECU/ECM and as far as I know DCJ does not touch that other than with the F-37 engine detune and the ECU/ECM does not just reprogram timing such that timing needs adjustment all by itself.
You might drop Keith at GDE a note but I'd look at a) drop in a new GM MAP sensor as that's cheap; b) carefully inspect wiring to MAP and MAF including wiring inside the wire loom across the top of the engine as chaffing has been reported; and c) find another place to work on the vehicle as this dealer doesn't know what they are doing. With respect to c) where are you located maybe there is help nearby.
If you are tired of dealing with the dealer (who are you using by the way?)....give Jerry a call at Global Off Road and Diesel a call. Their number is 919-784-0411. They did my timing belt job and they were very reasonably priced for the labor (I supplied the parts). He has dealt with CRD's in our area and I'll go back to to him for service I need. They are off Barefoot Industrial Drive off of Glenwood Ave not to far from the Angus Barn. Hope this helps.