I don't know that there are Gronks and Grahams this year. It wasn't hard to see Gronk and/or Graham as possible breakout candidates (there were tons of articles on and tons of buzz about both guys). Both guys had done something to generate buzz already, and were in situations where their workloads looked to expand. But it isn't every year you get breakout candidates on offenses that ALSO have a legitimate shot to be legendarily prolific.
This year, as long as you're not married to TE, you could consider Brandon Lloyd one of these guys. Great hands, familiarity with the offense, should be operating in a part of the field where he's going to get the lion's share of the work, and oh yeah, his QB is a legit 5000/50 threat. Obviously though, only has so much upside, since he's already targeted fairly high.
I posted earlier that I see Malcolm Floyd having this kind of "radical leap upward" potential. He went from a situation of uncertainty in SD's WR depth chart, to one of relative certainty with the injury to Brown. He's got good rapport with Rivers, and this passing offense puts up huge numbers annually. Could realistically double a lot of the projections I've seen for him.
Among TE's, there are only two guys I see who have a history of doing pretty well with what they've been given, AND are in position where their workloads might legitimately expand...where history also says that workload might expand to pretty huge dimensions.
Greg Olson is one. I can't honestly say I'm a huge believer. BUT, Olson + Shockey combined made for some pretty awesome numbers, AND defenses seem to have learned to take the over-the-top stuff away from Cam, so the short game may even expand this year, AND of course Shockey's gone. I don't think Olson has Gronkish upside, but I could easily see him moving into the tier right below that.
The other is Pettigrew. Obviously plays on a ridiculous pass offense. And is frequently the Lions' clear cut #2 option. Had a strange disappearing act for a month in the middle of last season, which brutalized what would otherwise have been really awesome year-long totals. Can he get his head screwed on and bring it every week? Early in the preseason, it looks like Stafford still has confidence in him. He doesn't need to take a huge step up...just needs to stay focused and healthy. If he does, he just might be able to hold off Titus Young as the 2nd biggest target hog on the team, and 1000/8-ish numbers aren't out of the question.
Of all the other good bets late at TE, there aren't any where you won't be relying on significant growth or situation shifting if they're going to emerge. Gresham would have to improve...Kendricks would have to improve...Fleener would be a shot in the dark with no supporting history...for Tamme, you'd have to believe in Manning (which I don't)...Davis and RG3 have no history...Cook would need a huge and unexpected spike in targets...etc.