Then it's almost as if you were riding a bucking bronco! I can take it over one hundred if I ease it up, but if you tried to hit passing gear, it would buck, shake, and physically shudder. I am thinking it is somehow connected to a vacuum problem. I've noticed on occasion if I start it up, throw it into reverse to back out of my driveway, when I hit the brakes to put it in drive, the brakes are non-existent. However, from that point on the brakes and the brake booster seem to be working fine. I purchased some MAF cleaner and am getting ready to check that!

 

Sounds to me like you have one or more coil packs failing. Change them all along with the spark plugs. The coils will often fail under load but not at cruising speed.

https://www.ebay.com/itm/6-Ignition-...acks.TRS0.TSS0

 

I agree with the weak spark as listed above. But in addition, sometimes in a lean condition the engine will back fire back through the throttle body (bucking bronco). This could be from a vacuum leak, or a fuel delivery problem like fuel filter.

As a beginning, pull the spark plugs and see if they are super bright white and clean, which means they are overheating. Then you know it's running lean and you can diagnose further. If they are brown or black, then you likely have a misfire.

The brakes fading sounds like there may be a vacuum leak in the servo hose or nearby. Typically you should have two or three good pumps of the brake with the engine not running before they get really hard. If you don't, then you most likely have a problem.

The brakes and the engine misfire may not be related.