engine problem

[dan the man]

hi! i am having "pulsing" or "serging" on my engine when going down a hill when driving over 80 km. an hour.

I cant seem to maintain the speed limt if i try to keep my foot on the accel. the engine starts jerking and the tach. is jumping 500 rpm. up and down. If i go down the hill in neutral, the tack stays at 800 rpm. and ther is no jerking. If i try to put the trans. in drive not over drive, i again start to jerk and the tack. goes nuts.

When i go up the hill its fine. Any kind of input would sure help. I drive a 2000 H1, it has 180 thousand km. It also has a new trans.Hoping someone out there has had this problem before and fixed it. thanks for the help.

[dan the man]

thanks for the input mudhog, Ijust installed a new trans. the fluid is topped up nicely. I am not getting any codes on . I will look into the speed sensor and vacuum solenoid. Thank you very much for the direction.