Can ANYONE please help ASAP!!

Ok, so we just picked up a new to us Grand Cherokee, and I found one little problem. I hope some of you can help me out! It has the Quadratrac 4.0L and is a 2001.

When you completely push the accelerator all the way to the floor when taking off, all is good. Until you reach the top of the power band and rev it out, but it will not shift to second. It just bounces back and forth on the rev limiter and still wont shift. It is in Drive and not first.

Any ideas what that could be?
I know that on my XJ I can change the shift points, can I change that as well on the Grand? Can anyone please help me, as I want my girlfriend to be as safe as possible!

Thanks all!!

hey buds, does the GC run fine otherwise? if you only have this problem when your floor it to accelerate I would say just don't floor it. Or if you need to, floor it, but when it won't shift up, take your foot off for a second, let if shift and continue on your way.
That may not solve your situation long term, but maybe help in the mean time.
Hope the weather ain't as hot in the GTA area as it has been here, gonna be in the 'Shwa for the long weekend.