By tri-axle I assume you are referring to the fact that the JTDm has three axles/shafts, one to each wheel and an intermediary one to extend the gearbox/differential to the right hand shaft/wheel. It could also mean the three ended joint on the inner end of each shaft. Anyway, both the wheel shafts are identical. I've just experienced this judder at motorway speed, 70-80, especially when powering on a hill or overtaking. As it only happens with power applied, and as its highish speed dependent, its definitely drivetrain related after the Gearbox. If you keep your hand on the gearstick while accellerating you can really feel it. All the blogs point to this, but the use of the term tri-axle is confusing. My money is on the three lobe joint at the gearbox end, these are also know as spider joints. If your CV joints were knackered as it seems, then its likley the joints at the far end are worn. One blog refers to replacing the cups also, these are the tube ends out of the differential with the hexagonal hollow shape inside. I've attached a picture of most of the driveshaft components. The spider is part no. 46308126, the cups are, long shaft 46307865, short shaft 46307522. The spider will cost a lot less (about 70) than buying a full shaft. The cups are pricey, 130 -160 maybe. I think the nearside one is more likely the one to replace.