Po 118 code comes up replacedthemostat ect sensor temp gauge does not come off 100 makes check gauge light come on then service engine light also cruise control stops working sometimes

SOURCE: NOT SHOWING TEMP ON GAUGE,ENGINE LIGHT IS ON,FANS

You may want to check out http://www.obd-codes.com/p0128 it has some good info on your problem.

SOURCE: 2008 gmc sierra 1500 crewcab.

Hi,

A vehicle may be brought into the dealer for a reduced power message, and DTCs P0120, P0220, P1516, P2101, or P2135.

The Throttle Actuator Control (TAC) / throttle body type trouble codes may be caused by a loose wiring crimp at the throttle body connector, or a broken throttle body circuit.

Complete the current SI diagnostics for any symptoms or trouble codes found. If a intermittent T/P or TAC module type code is occurring complete the inspections below.

Inspect all related throttle body terminals for a loose wiring crimp. The loose crimp may be difficult to find, and the poor connection will be between the terminal and the copper strands of the wire. Wiggle test the individual throttle body circuits to see if the concern can be duplicated.
Inspect the related circuits for broken wires inside the insulation. The outer wire insulation may look fine, but the internal copper strands may be partially broken. Breaks in the wires usually occur within 1 to 4 inches of the throttle body connector. Wiggle testing may also induce a trouble code to set.
On C/K trucks complete SI procedures for voltage drop on grounds G103 and G104. Grounds G103 or G104 may be loose or corroded.
If a terminal crimp or a broken wire has been found, repair or replace only the circuits involved. There is a throttle body pigtail connector available through GMSPO, but installing this pigtail connector may cause other intermittent TAC module/TP codes at a later date. If this pigtail must be used, please follow the SI procedures for Splicing Copper Wire Using Splice Sleeves. (the proper Kent-Moore crimping tool must be used for this repair)

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

Please get back to us if you have any further query or else accept the solution.

Thanks for contacting fixya.com

SOURCE: Envoy 2005 XL Cruise control not working

Your dealership should have seen any underlying codes. Most Cruise controls I've worked on are used on the vehicles vacuum. that is where i would start, because on a grade your engine uses more vacuum pressure thus taking from some where else.

Testimonial: "Thanks, will check the vacuum lines to the cruise control to see if they are ok."