modulators are easy to replace, but will NOT help your situation. because the vacuum modulator does NOT have anything to do with the engagement of the gears
it acts as a throttle "sensor" to restrict or unrestrict a passage of oil- altering pressure in that passage. so you have several spool valves that have 2 opposing pressures on them.
on one side you have throttle pressure, and the other side you have governor pressure.
the governor is a centrifugal device that restricts or unrestricts another oil passage, in relation to vehicle speed. these opposing pressures tell your transmission when to shift and to what gear. its a balance of "engine load pressure/vehicle speed pressure"
and therefore has nothing to do with gear engagement. what you're experiencing is totally normal because when you shift into forward or reverse it puts load on the driveline which takes up any slack and causes a clunk. if you're worried the clunk is too loud and there is too much slop? crawl under the truck and shake the driveshaft to see if there is sloppy u-joints or pinion bearings. make sense? don't buy a vacuum modulator
