I wouldn't be concerned. The GM transmission used is adequate to the GVWR/GCWR of the chassis and the torque output of the 6.0 liter gas engine.
You might enjoy the better ergonomics of the Express cab, about 6 inches longer than the Econoline, with the engine even further forward, for less engine housing and more footspace.
Think about whether you want to tow, the GCWR might be less than that of the E-450. However, a 2900LTD on a Ford chassis might be an E-350, which also has lower GCWR than the E-450.
About the coach itself, it was when new about the best value in the "family of six, no slideout" category, comparable in cost to FourWinds 5000 28A. The LTD was made to suit the needs of rental dealers, meaning they were fully but not extravagantly equipped at the base price, and had rugged, easy-care trim materials. The big market, however, was simply families that wanted to get into a C that size at the lowest possible price, and most were quite happy with what they got.
