My 99 yukon just shut off while driving and wont crank back up

google that, you can find it

Won't start how ? When you turn the key to start does the starter engage the engine an spin the engine ? Crank - no - start or a no crank - no start ?

if the starter spins fast, and cranks shaft is dead.
the starter is bad, or more exactly the pinion drive is dead.
but that is 99% the solenoid (starter bad)
replace or clean the solenoid drive,
make sure the pinion slides easy. there.

Sounds like you will have to replace the computer. The mechanic should have cleared the check engine light after he worked on it.

Your car is 18 years old. It's likely history. Sell it as is for what you can get.

Take a fuel pressure gauge for a ride --tied to wipers

See if your loosing fuel pressure when it quites ,or see if
that data is avail on scan tool

Some brands of pumps don't last long,so I heard & see from
other experts on here

I guess a relay for fuel pump could have a bad primary coil in it

Try switching them around-- to something else you don't need
all the time

When is the last time you had a tune-up on your truck? During the cold winter months, if the battery does not have a proper level of cranking amps it is sometimes hard for the engine to turnover in the cold. You may need a tune-up or battery replaced.

Fuel pumps are real common to go out on those vehicles

bad mass air sensor could be the culprit...it is by the air filter, be sure hose is secure and clamped

use a timing light to test for spark
have spark: timing belt broken