Hi guys, I have a 2002 BMW X5 4.4i 160k miles on it.

It's a beast and it impresses me every time I drive it until recently.

One time, as I was going home. Everything was fine, then I suddenly felt like I was dragging something. I pulled over at a gas station and everything seems fine. I revved it good and sped up good. Everything was going great until the last stoplight before home. As I accelerated from the stop light, the car seemed like it had a sliding clutch. The car was shaking and the gears seem to fail to engage. It revved over 5k rpm on Drive with nothing happening until the "Trans.Failsafe Prog" popped up a good 7 seconds later. The car seemed to be stuck in 5th gear and can drive just fine on that mode, just not the accelerating part.

After restarting, the failsafe is off but the SES light is on. I tried driving normally but every time I rev beyond 1,500rpm, the car just shakes and won't cooperate until the failsafe prog comes up again and I'm back in 5th gear.

What's weird about it is that when the program is not engaged, I could not do much with Drive, but Reverse seems to be very responsive.

It's 100F here, right now, so I doubt it's the cold like some people suggest. Please help. I've read some people attribute it to DSC modules and alternators, but they seem to have never experienced the shaking and sliding scenario.

Please advise.