With regard to dead spots, now I see the reason why: the scanner you are using is an older model P25 Phase 2 scanner (BCD436HP) not designed to handle simulcast well. A good majority of the tower sites along the Garden State Parkway have now been switched over to simulcast type, and are no longer the ASR type (single broadcast sites) like what Telegraph Hill, Neptune, Galloway, and some other ones used to be. Using my SDS100, I do not encounter any dead spots with the SMA style antenna. The stock antenna sometimes might hit a brief dead spot, but that's because it's designed for all bands, and not specifically just for 700/800 MHz coverage.
In Ocean County, coverage was poor in some areas, but with the improved simulcast coverage and some antenna modifications recently (within the past year), I have noticed coverage to be far more superior. If you are using an older P25 Phase 2 scanner, reception has actually become worse since simulcast distortion is present. What a BCD325P2, BCD436HP, WS1080 and TRX-1 used to be able to receive has significantly become worse to the point that the reception is spotty at best, based on my experience while hiking and driving in those areas.
If you scan the NJ Turnpike Authority 800 MHz system with the BCD436HP, reception should be excellent since all of those sites are ASR (single broadcast type) that are networked together based on subscriber affiliation. There are no simulcast issues with the NJTA 800 MHz system, so if you compare both systems (NJTA & NJICS) on your BCD436HP, you'll notice the differences between how simulcast and non-simulcast (ASR type) work. When the older style P25 Phase 2 scanners were originally designed years ago, there were not a lot of simulcast systems in play at the time.