this only happens if it sits for long enough to completely cool, like overnight or 2-3hrs. the RPMs continue to climb 4000-4500 and 40-50 MPH, without abusing it I let it slowly wind out and it shifts. After this first take off it doesn't do it. Even if I manually go through the gears it still won't shift until it desides to, the RPM and MPH vary so its not linked to that. The fluid level looks good. is there an additive that might help reduce or eliminate this issue.