Hello! I am new to this forum but always love taking advantage of knowledge and expertise on other similar vehicle forums. Reading through lots of posts, this LS1tech forum seems to have some very helpful users. (The worst by far are Honda Civic type forums where its just a bunch of newly minted DIY mechanics who because they installed a K&N air filter are therefore self proclaimed experts)

I am trying to help my father-in-law with his 01 Camaro with 4L60E auto trans.

Background: 01' Z28 with approx. 75k miles and driven gently practically its whole life. Vehicle won't shift to 3rd or 4th. I would describe the attempting shift feeling as if when driving a standard you are pressing the clutch in about halfway while still pressing the accelerator. Never shifting, RPMs increasing, and losing or barely maintaining the same speed. According to father-in-law it only made a few (4-5) 'odd' shifts before not shifting anymore. I caveat that statement because he isn't car savvy at all.

So far: No engine codes specific to shift problems (I believe it has both catalytic fault codes). I dropped the trans oil pan and checked the resistance across both shift solenoids (exact same), then just to double check I swapped the 1-2 and 3-4 shift solenoids with zero impact on the shift. In dropping the trans pan there was zero visual indication of wear (no metal bits, shavings or sparkle).

Father-in-law is currently driving it around in 1st and 2nd only, not D, to prevent the car from continuing to attempt upshift. Other than high RPMs at highway speeds this shouldn't be terribly damaging to the engine or trans?

Thoughts: From reading similar threads the problems appears to be likely the 3-4 clutch pack? Seems it is a common issue with the 4L60E transmission. Are there any other possibilities? Any other checks or tests I can run before investing in a clutch pack or used trans?

Assuming clutch pack: Any suggestions on upgraded parts? http://www.summitracing.com/parts/tci-374090/overview/ Just an example price line and seeming upgrade.

 

I've had good results with the Raybestos Z pak.

 

I would stay away from the 9 friction kit in that Summit link. While some performance builders like 8 frictions, others prefer only 7 because the frictions and steels are then much thicker.
If you are going to try the rebuild yourself, I would recommend a basic 4L65E rebuild kit as that includes 7 frictions. A 4L65E kit sometimes includes nice BW HiEnergy or Raybestos GPZ 3/4 clutches, but often clutches a step down from those.
Raybestos seems to be trying to promote the GPZ frictions in place of their older Z-Pak. When installed by a pro mechanic, they guarantee the GPZ frictions for 100,000 miles, parts -AND- labor.