At 28 you have been able to purchase an additional basic attack for 8 levels (and can purchase another soon). So the first thing you should do is go to the gladiator guild, do the quest they have available for and get that (you got an NPC linkshell alert at 20 alerting you to this btw you must have missed it, but it is glowing in the corner of your screen until you read it, and there is a chat alert).
Anyways what I think you should do during battle as a Gladiator, is start the fight out with invigorate (which all melee should do). Get guard up, and as soon as you get a block hit Phalanx. Then either use a 500 TP ability, or another basic attack to get more TP. Refresh guard, and put up outmaneuver (increased TP from blocks) and use a defensive ability (sentinel, featherfoot for example). At this point you should have plenty of TP use raging strike/ferocity and a 1k TP weapon skill.
This is just an example, you can use other abilities as well (though if you are tanking I would suggest to use Phalanx liberally), but you should be fitting in many more abilities than you seem to be currently. When I played Gladiator from 20 on I was never spending more than a second or two not actually using one ability. In fact gladiator is by far one of the busiest classes in the game in my opinion.
This isn't a personal dig, but all you people complaining about auto attack should really take a look at your class forums for ideas on what you can do rather than "waiting for TP" before coming to the general forums and complaining about the system. I understand it is easier to complain about something, and I certainly don't mind giving people tips on the forum or in game; but the best thing you can do for yourself in an MMO is to either try various combat strategies yourself or read what others are doing (or preferably both of these things). There will never be a good enough tutorial in any MMO to teach you how to play your class as well as doing those things will.