There are lots of ways to fight it, but you really need more information on what type of radar, etc. he was using. The police are legally required to give you this and other information (model, calibration info and dates, etc.) upon request (even after the fact) and your ticket will be thrown out if they cannot provide it since you are unable to reasonably defend yourself.
One of the interesting things will be the type of radar used. If it is the older style, the radar will not be accurate enough to differentiate your car from the semi, and would return a reading from the largest object in its bandwidth. Many newer non-laser styles of guns will still get severely distorted results from large objects including trucks, road signs, and trees.
Another interesting thing would be to see if in the officer's notes he says the radar gun read 98 or what. If it says it read 98, you should get it thrown out since he was moving and would mean you'd be travelling around 75 mph. If you were theoretically going 98 and he was travelling 75 mph, it is possible the reading would have had to exceed the maximum reading for the gun!