99 Chev Suburban 4x4 5.7L - Not sure if Electrical or Mechanical Transmission issue. Runs fine in all city/highway situations until I punch it at highway speed to climb hill or pass. Pass gear engages smooth but then will not disengage. Tach gets up to about 3k, no torque, then rear end starts bucking like a wheel is coming off. Let off gas, go to Neutral, rev a few times, get the RPM down to normal, ease back into gear and take it easy, everything fine. No residual problems whenever this happens, just like a "DON'T DO THAT AND ALL WILL BE FINE" But sometimes you need that passing gear, Transmission and all boxes recently serviced and mech said no problems. This has been going on for over 4 years. Started out as spark knock in same scenerio as described above, mech changed the distributor (equivalant part) and seemed to be fine for awhile, now acts like described above. Thanks.