Originally Posted by phunk

Skipping gears is hell on your synchros. It worked before because they were fresh, it doesnt work now because you are wearing them out. Pretty soon you will have trouble shifting into 6th at all without double clutching. Many dealers will reject warrenty replacement of transmission with synchros problems if they find you skip shift gears... they would know because someone might complain that they are no longer able to do so, or they will ask you to take them on a drive to show them the problem, but they are also observing how you drive.

If you are hell-bent on continuing to skip shift 3rd to 6th, instead of depending on whats probably a single brass synchro for 6th to slow the mainshaft down by so much for such a change in ratios, just double clutch it and you are removing most the burden of the synchros. double clutching takes more time but if your skipping 3-6 then you arent racing anyway.

ALSO i would like to add that I am not a transmission builder, so my terminology shouldnt be quoted or used for debate and i will gladly take a seat on this topic to a transmission expert... i am just explaining it the best that I can based on the little i know about one aspect of cars/performance that i have rather avoided learning the deep inner-workings of.