When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I'd suggest before you tear anything down that you change the transmission fluid. Getting the old stuff out and replacing w/ new could make a difference. I went with the GM lubes but that's just me as I had heard that '99 MN6 have syncros that don't do well with synthetics. Check your manual but you'll also most likely need about 8oz of anti-slip additive.
I'm having a hard time getting to reverse as well. I need to use both hands. I played with the adjustment and it made it better but still difficult. I emailed RPM Transmissions and they suggested checking the lockout solenoid. Haven't looked into it yet, waiting for snow to melt here. It happened at the end of season last year. I was at the strip and after a run had trouble backing into my pit spot.
A little trick I learned long ago was to push clutch in, put shifter into third (since its the easiest forward gear) then take out of third and slide over and into reverse. Goes in easier. Done this since 2000 on various LS1s, seems to help.
If you have a real problem it may not help, but try this before trying anything else.
The first sign of my transmission dying was the loss of my reverse gear, then came 5th gear....if you track your car, I highly recommend getting an RPM Level 4 Transmission - worth the investment. Mike