I put in a Transgo SK C5 that is for 73 and up C4 and C5s. I tried that with an H servo and a new green stripe modulator to try and improve the 2-3 shift, but none of that worked. When I put in my junkyard special 302, the 2-3 shift really got bad under acceleration.....and I finally decided that there was no option other than rebuild. I had expert help though, as a friend of a friend let me re-build it in his shop, with good lighting, a solvent tank/parts washer, stainless steel table with a drain......lol, I was spoiled. I washed all the pieces, and put most of it back together under supervision. I, in return, built the guy a hand built brass 1/24th scale slot car chassis (these take about 12 hours to build from scratch) that our club races.....so I got an A-1 rebuild and he got one of the finest OSCAR club slot cars available. ( Blah-brag-brag-blah) I had the converter rebuilt and tuned to be a high stall stock converter....supposed to stall around 1800-2000. I kept it conservative, as I think my engine has a fairly wide power band. If I give away some potential off the line, I'll just call it traction control. I really need to get to a track now and let er rip for a 1/4 mile.