fairly worn out on the higher mileage cars by this time and need a rebuild. Welded diffs are not a long-term solution and put stress on other things needlessly. Even in peak form, they tend to overheat and become inconsistent on prolonged aggressive use. Rid yourself of all the old bushings front and rear as they create slop and shift around, go with polyurethane or Nismo bushings where applicable. Some locations don't react well to the poly bushings since they tend to bind up a bit easily. So make sure they are installed on a pre-loaded suspension. You need to eliminate chassis flex & twist (bracing) along with the suspension to transfer the energy consistently. Also, make sure you are addressing any cooling issues you may have. Driving sideways does not direct airflow through the radiator efficiently, and cars tend to overheat. Ther are many more things to look at, but that's a good start. Are you running a TT or NA? 2+0 or 2+2?
1993 Nissan 300ZX Slicktop (Oxford Gray Metallic) 1992 Nissan Skyline GT-R (Gunmetal Gray) - Long Live the Z and Godzirra! - "Love cars. Love people. Love life." - Mr. K.