I think one of the things that pulls TruSorc away from high magic is that the lower level powers are mostly very... not-flashy. A standard first-level wizard can do things like Burning Hands, Jump, Magic Missile, and Mage Armor. A first level TruSorc might be able to do force damage... but it'll be nonlethal, and won't automagically hit. Burning Hands is out of reach until Create Element at First Magnitude, while the spellcraft required to produce Mage Armor (+4 AC for an hour) is well out of the range of a first level TruSorc. Jump isn't possible until 10th level with Enhance Person.
With that in mind, one thing you could try would be shifting certain talents down a magnitude for purposes of learning them and base DCs. For example, in a high magic game, healing should probably be available before 5th level. Likewise elemental damage. Enhance Person and Obscure could both be dropped to First Magnitude from Second; they're both available at 4th level for standard Sorcerers, so opening them at 5th for TruSorcs would bring them a little closer in terms of power availability. Changes like that might be what you're looking for.
However, I will say that high-level TruSorcs don't need any help being high magic... I recently found that a properly prepared 20th-level TruSorc could beat a spellcraft DC of over 7000, which is more than sufficient to build a spell capable of killing deities with nearly high probability. Granted, you die in the process... but a caster of that power is easily able to cast a contingent resurrection on himself beforehand.
A 15th+ level TruSorc is likely to be running a pretty big defensive buff suite (I tend towards Reflect to stop enemy spells, Obscure for general miss chance, Force, Protection, or Enhance Person for +AC, and Wards for elemental resistance and DR), has access to good general purpose enhancers (Enhance Person, lots of Foresee, conceivably Enhance Item), and can take out opponents even with low-level powers because save DCs scale with class level (Afflict is a perennial favorite of mine. For under DC40 spellcraft and a will save, you can blind, deafen, and deny sense of touch. While they're flailing uselessly and biting their own tongues off, the fighters kill them. Also fun is an emanation of Afflict in say, a 10-foot radius about yourself with the same sense-denying effect. Enemies close to melee? Will save or useless.).
Some of the mid-level terrain control powers really open up offensively at high levels (Air Lore for tornadoes and Earth Lore for earthquakes, respectively), and the Third Magnitude offensive talents are pretty brutal on their own (see the above Afflict Emanation, except with Fort save or die. If you're really worried about enemy melee, use both Afflict and Slay emanations at once).
Finally, when you combine Time Lore for 5-round guaranteed Time Stop at 15th level with the ability to cast both a swift and full-round action spell every round, you can really unload (or insta-buff your friends with whatever is most useful given the opposition, or control the battlefield in ridiculous ways, or pile emanations onto yourself and teleport into the middle of the enemy, or do whatever you want, basically).
Effectively, high level TruSorcs are easily on par with high-level standard casters, and are significantly more versatile. Just make sure you bring friends with healing to keep you conscious...
So I guess the thing is that True Sorcerers scale from low magic at low levels to really high magic at high levels. Be careful if you change anything; if you scale up the low end, you may inadvertently scale up the high end, too.