The problem of creating suspense in first person is a difficult task indeed. So hard in fact, I have sworn off writing first person pov to create suspense. Huckleberry Finn was written in the Single POV, but it was not written in a first person approach that keeps us continually reminded that the "I" character is any different from being told a story in third person. This is the secret, I feel to truly good first person narratives in general, and that is we are made to care about the main character...and we are never bored at listening to his voice. Voice is the secret to successful fiction and is the main ingredient no matter the point of view. While I prefer multiple pov's to a single pov, most PI novels are written in the single pov, and I suspect most are first person, whereas many other categories of the suspense novel are mutliple viewpoint utilziing many voices, including that of the killer or villian.
What pitfalls there are in writing in first person exists in third as well, and the major pitfall is slipping into using pronouns ad nauseum until we forget who the character(s) name(s) is/are. In first person it is I, me, my , myself, mine...and more I's all over the map, often three and four in a single sentence. In thrid it can be he or she all over the place. A reliance too heavily on pronouns can kill the quality of the voice. This is a numbe one sin in using first person in most bad writing in my opinion.
At any rate, whatever you choose to use....look into Making Shapely Fiction by Jerome Stern for the finest discussion on how many varied pov's we can choose from and a terrifict discussion on such issues as first vs. third pov and voice. Best honest talk and most succinct covering the entire range of choices we have as authors is in this little book--my Bible.
Robert W. Walker