What trans is this? A 4t60? As Bill said, a rebuild is not cost effective because of the tools involved. however, there are options. First, does it go in to 3rd and slip, or not go in to third at all? What happens here will determine the problem. If it'* slipping, then the clutches are gone. If it'* not going in to 3rd then I would drop the pan to do your filter fluid change and take the extra step to pull the shift accumulator. Open that up and inspect the 2-3 piston. Could be a blown O ring which would cause the fluid pressure to not get high enough to engage 3rd.
SAVING THE WORLD ONE BONNEVILLE AT A TIME
1997,1998,2000,2005 year confused Bonneville SSExi. Stock? ish.
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