can not keep bolts tight

[terryggoround]

so I have a 1970 gmc jimmy 4x4 and just had a new rear driveshaft built and installed. The problem I have been having before this was done was various bolts keep coming loose. The exhaust down pipe bolts , the valve cover bolt, the bolts on the cross brace for the engine and transmission. No matter how much I tighten and even using lock tight the bolts still come loose after a few weeks. The truck is a 1/2 ton with a 350 V8 and a 4 speed manual transmission with 1st gear is a granny gear. The rear driveline was changed to a 1 ton 1350 series. Any suggestions would be greatly appreciated. Also I noticed the the brace that attaches to the frame and the transfer case is not there. could the weight of the tranfercase bouncing around be causing my bolts to loosen?
Thanks
Terry