1997 Silverado 4X4 computer problem?

Hi I have a problem with my truck starting it turns over has spark and gas but will not fire. At times it misses like it is out of time and turns
over at a high rate of speed. Does anyone have any suggestions as to the problem could be as I think it may have a computer problem but not sure, It has a freshly rebuilt 3500 with about 1000 miles on it. Any input would be greatly apprecaited as I can't get it to a service station. Thanks in advance for any help or advice.
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