I've had a problem where the truck seat was so flat that there was no possible way to get the proper recline on a Chicco, so it was not compatible, even though it did fit, front-to-back so that a passenger could still sit in front of it. I think the only option is to take your seat and try it out on your top contenders. What trucks are you looking at? It might be possible that another seat might work, too, like a low profile convertible like the Scenera NEXT or Graco MySize, those are good for babies as small as 5 pounds, as long as you can achieve the proper recline.
Good luck!