Runs rough after 45mph

tb34tb34 Member Posts: 1
edited August 2015 in GMC
My truck runs good till I hit about 45mph then cuts out (most of the time). I put in new plugs and wires and cap and button. Tried the coil. Changed out throttle position sensor still no luck. New fuel filter. Some one mentioned fuel pump but I changed it three yrs ago because it would not start. A mechanic hooked a computer up to it and said all the plugs are misfiring. Could it be computer? Can a fuel pump go bad and still start? Please help! Thanks.
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