Bought a 1996 Chevy 3/4 Ton and the transmission was jerking a little bit when shifting. Put some ZMax in it and now it is jerking harder. Don't know if ATF has ever been changed. Truck has 93,000 miles...
I wouldve tried changing the fluid before pouring in some random fluid.
I would, however, add a bottle of Lubegard Red after changing the fluid/filter.
PS: My local K-Mart has Z-Max A/T treatment on clearance for $5 a bottle. I don't know anything about it but I've had good results with LG Red.
And here I was thinking Zmax was for engines only.
Start doing drain and fills with the correct fluid.
You'd probably be best off dropping the transmission pan and cleaning it all out.
I'd almost guarantee all work has been neglected to this vehicle.
I would start by draining the fluid and refilling with Some DexronVI and letting that work for about 1,000 miles and drain it again. Another 1,000 miles drain that and drop the pan, change the filter and start working some Maxlife Dex/Merc in there.
No additives needed, but Lubegard red won't hurt. It's got LXE Esters, anti oxidants, Phosporus, and a little friction modifier in it.
Flush the transmission using only a high quality ATF. Many additives don't work, and should only be used to get a few more miles from a dying transmission. Z-max may be such an additive.
I have heard good thing about using the right Lubegard LXE additive, but I have never been a fan of any oil additive.