My C-4 was rebuilt with Art Carr guts about 5 years ago. The trans sat for that many years. I installed the other day with new motor. I noticed that if I ease up the rpm scale to above 2000, the 2-3 shift will rev. before it engages. This is fairly predictable. If I ease up to about 3K rpm, it will rev about 500 rpm between shift. Now, I 3/4 throttled this monster and the 2-3 shift at 4K rpm didn't skip a beat. Any idea what could be causing this?