When I am in park or come to a complete stop at a light , the truck idle back and forth and shakes the truck. I have service engine light with P0171 and P0174 code showing. Have cleaned throttle body, maf, changed pvc fuel filter, Iac

Define the issue a bit Further. does check engine light flash while stopped? check the basics is there air restriction and when where plugs last changed?

Is the check engine light on? Mountaineers are bad about developing vacuum leaks which will lean the engine out and cause it to stumble at idle while in gear. Check for p0171 and p0174 codes.

Could be a problem with the MAF sensor but if it is you should have a code for that too.
Other causes include low fuel pressure, and a vac leak or air leak in the intake hose to the MAF.
The codes mean the ECM can not make the injectors rich enough to make the O2 sensors switch back and forth.

P1131 Lack of HO2S-11 Switch ,Sensor Lean
P1151-Lack of HO2S-21 Switch ,Sensor Lean
PO171- System to Lean (Bank 1)
PO174-Systen to Lean (Bank 2)

Fuel Filter -Plugged
Low Fuel Pressure
Evap System -Leaks
Leaks - in ducting,air filter to throttle
PCV -Leaks
Exhaust System -Leaks
O2 Sensors-worn out

shaking while idling means that base of engine may need to be changed.

P0171 - is fuel system is to lean (Bank#1) Take the car back to who ever scanned it for you and see if any codes are now pressent in particular to the EGR Valve they range from P0400 up to and including P0409, or any other new codes.While you are at it make sure they erase the set code P0171 un less it is already don.If no codes show up on the new scan replace the Ignition Control Module not the ( ECM -on board computor).If new codes do show up follow up on them first. Good Luck.

did you check your transmission fluid

The most likely cause is that the rubber in one or more of the engine mounts has perished and split.
Check them by first parking the car on a level surface with the handbrake firmly applied and the gear shift left in neutral.
Then when the engine has cooled, lift the bonnet and check for excessive play by rocking the engine back and forth, this should reveal any loose engine mounts.

i had the same trouble, there is a rubber boot under the cover on the top of the motor, it is coming from the egr valve, takes about 5 mins to repair and less than 5 dollars.

bad intake not enough air to the cylinders, spark plugs could be a prob, or ur car is running to lean...i hate a similar prob with it shakeing when idleing but i just tap the gas and it stops