Converter lockup suggestions please.

[Longhorn 70]

I have a 700R4 in my pickup. It has performed well over the years. It was built and installed in 1997 and has gone through 2 motors and a lot of miles and worked well.

I like using the lockup feature of the converter for long cruises to save a bit more fuel and let the engine just purr at 2000 r.p.m. or so. It will only lock in 4th. I only have a toggle switch for the lock\unlock though. IF it is on, as soon as I go to 4th gear, it locks. So I make sure I go to 4th with light throttle pressure. I'd like to get a better set up for it that will keep me from having to reach for the switch and also make is so the wifey can drive the truck if she needs to. I have a proposed schematic below.

The way I see the schematic is...
Accellerate as I will and when vacuum levels off, a short delay after it goes to 4th gear will lock the converter when the master switch is on.

If I jam the brakes, hit the gas and drop a gear, the vacuum switch will unlock it and have to level off before the delay will let it go to lock again.

Does it look to make sense? If you would please, thoughts, suggestions, remarks, or bad jokes will be appreciated.