The reason cams go rumpity rump is beacuse they are barely making enough torque to keep the crankshaft turning. Get a cam ground on a 110 degree center for torque. In the Comp Cam's Xtreme Energy line, they have a grind, XE262H which is just starting to get pretty rumpity rumpity on a 350 which means it will be a little smother on a 383. I recommend you go 1 size up, but no more than 2 if you want lots of torque. I just built a 350 with the XE256H cam and it makes more torque than the stock cam everywhere in the rpm range but also extends the useable rpm range to almost 5500 rpm which is your goal. The 262 and bigger cams will have you running 6000 or 6500 rpm redlines to take full advantage of their powerbands. The Comp Xtreme Energy and I believe Crane Z product lines all use faster valve opening rates to maximize torque for a given duration meaning more hp and better driveability.