Jeep Grand Cherokee Problem

I have a 2003 Grand Jeep Cherokee with 71,000. Two days ago it started to surge forward and backward when around 55 mph. It was suddle enough that I could continue driving and it eventually stopped. Today when driving on the highway above 55 mph it bucked much more violently. Very jerky. There are no lights on the dash lit, no weird noises or smells. Just had a new theromosat put in. All gages on the dash are normal. Please help!

The problem may be due to a fuel delivery issue. You could try replacing the fuel filter first. If that doesn’t work then have the fuel pressure checked. The pump pressure may be sporadic.

Another possibility is a speed sensor or maybe a engine sensor is having a problem.