There are TSBs on Lockup Shudder out there. It is usually not a fluid issue. The Mopar parts to fix this problem has not been available for years. Transgo shift kits do not address the problem. I found another brand that replaced the valve spring on the lock accumulator and it fixed the issue. This was on a A999 lockup transmission I put in my Cuda. I wanted it more for the lower first gear ratio and the extra clutch and frictions over the 904. I am using ATF +4 with no issues.