Strafford, Missouri-based truckload carrier RBX Inc. and its equipment leasing affiliate, Humper Equipment, have filed suit against Paccar Financial Inc. of Bellevue, Washington. They are asking a Missouri bankruptcy judge to force Paccar to turn over 28 Kenworth and Peterbilt tractors it repossessed in late November amid an ongoing engine performance dispute with the global commercial truck financing company and its subsidiary, Paccar Engine Co.