robbiejames,had to read your thread 3 times?try to help as best I can.cant say if cleaning the ground will fix your vehicle.but clean it anyways and then check again,if it doesn't fix it you will probably have to replace the ipc.I do about 3 a week at the dealer.these problems might be related to the ipc,cant say for sure.you might have 2 different problems.looked at the schematics on the ipc and g108 is the only ground for the ipc.here is the bulletin.hope this helps.post back if you fix it.
Subject:Erratic Speedometer Operation or Speedometer Needle Shakes Above 60 mph (96 km/h) (Repair Poor Connection at Ground G108) #07-08-49-027 - (12/04/2007)
Models:2004-2007 Buick Rainier
2002-2008 Chevrolet TrailBlazer Models
2002-2008 GMC Envoy Models
2002-2004 Oldsmobile Bravada
2005-2008 Saab 9-7X
with 4.2L Engine Only (VIN S -- RPO LL8)
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Condition
Some customers may comment on erratic operation of the speedometer. Others may comment that the speedometer needle shakes above 96 km/h (60 mph).
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Cause
This condition may be caused by a loose or poor connection at Powertrain Control Module/Engine Control Module (PCM/ECM) ground G108.
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Correction
Technicians are to inspect and repair ground G108 as necessary. Refer to callout 1 in the illustration above for the location of G108. Refer to the Testing for Intermittent Conditions and Poor Connections and the Wiring Repair procedures in SI for more information.