So I've had my 2008 Rav4 for a few months now and I love it. It's the V6 AWD 5 speed auto. I did a drain and fill on the trans pan when I bought it with some Valvoline ATF. Works fine but I plan on eventually using this Rav4 to tow my boat. I've been doing a lot of research on these U151 transmissions. People have a lot of different opinions on what fluid to use, I'm wondering if any of the fluids make the shifts stronger/quicker. Mine slides gears like it's trying to keep a full cup of water from spilling over. It doesn't slip like its bad, just very slow gear engagement. I have read about the Sonnax Zip kits, does anyone have that? Does it make the transmission snappier? I've had 2 Mustang's in the past with built autos that shifted so hard the tires would break loose, I don't need it to be THAT aggressive but how it is now I don't know if I wanna tow much with it...My boat may or may not be around 3500+lbs. I had a 98 4Runner that towed it no problem and this has like 100 more HP and an extra gear so as long as the transmission can hold up I wanna take care of it.