Well, the book to which you refer is GDW's Survival Margin: Gateway to the New Era.
Really, the CT to MT changes are too dramatic and yet, not so much. Describing them is easy, listing them is hard. It added a Task system, added Special Duty and Bonus Skills rolls, replaced many skill entries with cascade groups, went to a striker derived but not compatible combat system, added a striker derived but not fully compatible design system for ground, grav, and space vehicles, and added skill rolls to psionic tasks. Setting was thrown into a rebelion; later, the rebellion stalls into separate camps; and many areas blasted to near inhospitablility. Stats still 1-15 avg 7. Setting area expanded from Spinward Marches to Domain of Deneb, but Solomani Rim excluded. Uses reduced Jfuel volumes.
TNE changed skill aquisition to skill choices, but with similar CG rolls, and more careers. TNE changed the task system resolution process, dropping the time element, and using multiplications of a stat+skill asset for various difficulties, and introduced the first non-d6 Traveller engine, as it used a d20. It polished up the Twilight 2000 & Dark Conspiracy engine (which said polish was added back the other direction later). Stats are 1-15 avg 6, adds Charisma stat, as well. Setting is 70 years after MT's Hard Times, and Virus used to "Wipe the Slate"... Many CT and MT fans upset; man new players attracted by the Smash and Grab oriented setting resulting. Aging starts earlier, but is less profound; possible to generate characters far less hurt by aging at more advanced ages. Setting changed to the Reformation Coalition, near Sol-Gateway domain borders; Domain of Deneb added later, with drastic changes (so much for the Preserve mentioned in Survival Margin...). Uses semi-realistic MDrives (HEPlaR chided for unrealistically high exhaust velocities... near C...
T4 went to a variable d6 roll low system, with number of dice by difficulty. It also massively increased skills per term (from CT's 1-5 avg 1.3, MT's 1-8 avg 1.8, and TNE's 1-7 avg 3 or so; all are rough estimates) to 4-8 avg about 5. All CG tables changed to roll-low, and 6 skill tables per career, fewer careers. Used TNE's technical architecture. Stats 1-15 avg 7. Due to CGen and task system issues, strong tendency towards highly raised stats; C&D atts not uncommon. Setting supposedly reverted to "start of the Third Imperium" eras (Year 0, Year 40), but stats for systems mishandeled. Whole imperium (with mangled stats) presented with 1100 era borders... primary setting is Core sector. Adds back CT/MT style Thrusters (reactionless).
GT: 3d6 system, roll low, 4 stats (St Dx Ht IQ), 2 pseudo stats (Move, Will), point based CG, template based careers for those who need them, ship design in 500 CuFt spaces, similar to but not compatible with CT Bk5. Very different task system, as task labels simply modify Skill levels; Skill levels derived from Attribute+ skill "Level" (which may be as low as -4, and isn't defined as such). Loads of details in setting materials, setting is CT advanced sans rebellion to the rebellion time frame. Primary setting is Spinward Marches and Domain of Deneb. Numerous small issues with setting book make for annoyance of long term players; utility of supplements generally considered a plus.
HeroTraveller: Standard here is 3d6 Roll High combat, 3d6 roll low skills. Point based. 10 attributes, 8 figured attributes. Attribute range 1-20, average NPC is 8, PC base is 10. (That's stock hero.) Do not know what the standard setting is, nor the details, as it's brand new and I don't have it yet.
T20:
8 Stats, 1-20+, avg 10.5. Uses variant damage and combat systems from Traveller and D20, but feels fairly travelleresque. Setting is pre-CT by about a decade, and domain of Gateway, rather than Deneb. Design sequences derived from and compatible with CT Bk5, but many additions. Many supplemental materials dual stat CT & T20.
2300 (Traveller 2300, 2300AD): Not "really" traveller; uses MT aka DGP-CT task system but repacing 2d6 with 1d10. Choice based skill gains, no way to raise stats. Very much "Halfway between CT and TNE" (far more so than MT, really) mechanically; system creation rules are VERY different. Combat system very different very flexible, quite deadly. No playable aliens. Setting uses different FTL tech from Traveller line, as well as different STL tech.
by then of any sort. 
but at the far end of the Imperium in Gateway. Another Solomani-geneered race has been added to the mix, and a Gateway-specific Minor Human Race detailed.
Those are the kind of things I wanted to know. 
