Hi all. have a 99 C5 convertible automatic, and since changing out the lame 273 rear gears to 342,s I have this slight slipping in 4th gear. Never noticed it before the change. After this happens a few times it shifts very fast and hard from 1st to 2nd. Then I reset the codes and it's ok. Have a rebuilt tranny waiting to go in just in case that is what the problem is. just do not understand why it is happening after the rear gear change. any info would be great.