A "Last Train to Clarksville" Cuebid (LTTC) is normally a cue of the suit immediately below game, sending a general message of lingering interest but inability to personally take that next step. Thus, for example, in an auction where hearts is agreed as trumps, a 4D call in many sequences will usually send a general message that the cuebidding so far as suggested that slam is possible but that the person bidding 4D does not have sufficient information to justify entering the five level. It is a stronger bid than 4♥.
However, a strange sequence sometimes develops where the bid immediately below the agreed suit should actually be the weaker bid. The classic situation would involve a two-under super-acceptance. Consider the auction 2NT-P-3D-p-4♣-P-??? Responder will usually want to re-transfer via 4D to have Opener declare, planning either to pass or to make some move (RKCB or something else). So, this seems to deprive Responder of LTTC, right?
Nope. On that rare tweener hand, Responder simply bids 4♥. The cost of this approach is the loss of the transfer effect, but that may be a no gainer anyway. Much better, anyway, to limit the non-transfer to LTTC sequences rather than to save LTTC but lose the re-transfer on all of the clear game or clear slam try sequences.
So, if the normal LTTC call would be a re-transfer, then the actual bid is slammish.
Another sequence worth considering; similar principle. Suppose that you have some sequence where, for instance, spades are agreed but 3NT asks for shortness. An example I would run into might help. After a Jacoby 2NT raise of a 1♠ opening, we use 3♠ to show a light splinter. 3NT asks for the stiff (bid the stiff).
So, in my example, if I bid 4♣ (stiff club), Responder could cue 4D or bid 4♥ as LTTC. If I bid 4D (stiff diamond), Responder could bid 4♥ as LTTC. However, if I have a stiff heart, I deprive partner of the LTTC bid. What's the solution?
Well, when the highest option in responding to an asking bid is in the suit immediately below game in the agreed strain, the person answering the question should distinguish the highest answer as "this answer and I like my hand now" or "this answer but I am unhappy about you asking stupid questions." Sort of like wrap-around answering to yummy toes.
So, which is the stronger call? Well, that's a partnership agreement. One might use steps (first step answers with disdain; second step answers with jubilee), in which case bidding the trump suit is sorta like LTTC. Reversing this meaning might make more sense, for a couple of reasons. First, you might want to minimize the chance of a lead-directional double unless you have the good hand (relevant when the future dummy is answering). Second, maybe bidding game sounds like a weaker bid to your usual style. Plus, maybe bidding game on the weaker hands syncs better for when partner is (or you are) lost in the auction.