No. Hill was standing on the running board at Z306. Clearly stated there were only two shots.
Show us where he said there were only two shots. He always said he heard only two shots. He has said many times that he accepts that there were three shots. He has always maintained that JFK reacted to the first shot by hunching forward and to the left.
Re: standing on running board at z306. We do not have a visual record of when Hill stepped off the running board. We know it was after Altgens 6 at z254-255. It is difficult to estimate how long it took for him to get along-side the front of the QM when we first see him in the Nix film. He does not reach the rear hand-hold until z338 which is 4.5 seconds after Altgens 6.
I expect that when he stepped off the running board and hit the road, he was not immediately running at the car speed and probably went back a few feet before running faster than the car. If he left the car at z265 that would give him 4 seconds to make it to the back of the limo at z338.
If he leaped off at z307 that would give him 1.69 seconds to get up to speed and dash the 14 feet from the running board to grab the handhold:

That is not much time. He would need to
average 20 feet/second or 14 mph from the time he jumped off the running board until reaching the hand-hold (assuming the limo was moving at 12 feet/sec or 8 mph).
I would suggest that 4 seconds is probably closer to the actual running time.