I have suspected and this morning verified, that the springs on our Bigfoot were “frowning”.....no longer “smiling”! ?? The result of a “very” heavy RV sitting on underrated springs for 10 years! Internet research showed that on the E450 chassis, two spring packs were available....a 5100 pound and a 7200 ( HD pkg.) pound. We have the 5100 pound springs. Will be ordering new springs soon.....another RV related project ??! Will likely upgrade the front coils also.....it looks like it’s “cold-trailing”, while traveling down the road! ??