54K miles on E450 V10 is moderate and not concerning. V10 engines commonly exceed 200K miles. Check maintenance records and get pre-purchase inspection focusing on overall condition.
E-350 and E-450 use same V10 engine with nearly identical 8-10 MPG fuel economy. E-450 has heavier suspension, brakes, and higher GVWR. Choose based on weight capacity needs, not fuel economy.
Your engine stalling when rolling to a stop combined with inconsistent transmission behavior suggests issues with idle control, torque converter lockup, or vacuum leaks. The intermittent nature points to specific components that need diagnosis.
Yes, there are aftermarket transmission controllers available for your 2007 E450 that can hold it in Drive gear. The most practical solutions include installing a manual shift valve body kit or an electronic transmission controller.
SDI E-Clik owners report noticeable body roll reduction and improved handling. Expectations should be realistic - its good for the price but not a full suspension replacement.
A steering stabilizer helps reduce wander but is not always necessary. Complete the Quick Fix and basic checks first - a stabilizer masks problems rather than fixing them. If coach drives straight after maintenance, you may not need one.
Normal TorqShift V10 transmission temps are 150-200F cruising, up to 220F on grades. Above 240F consistently needs attention. Use tow/haul mode and downshift early on climbs.