Transgo Jr will allow C3 and C4 clutches to apply with full main line pressure ( 230psi) instead of control main pressure ( 124psi). It is helpfull to a certain extent but you still can't play hard without more pressure and better clutches if you run a programmer (tune). There is a lot more to this but enough for now.
But i do get the point like for OP he would have to drop trans to do the ratio-tek kit. But i still say its a lot cheaper than a built trans and makes it hold good for just moderate tuning like what the OP seems to be after.
Put in the trans-go, load up the ole 150 tune, lock it in 4th and let her eat. You will be limited to about 85 mph but you can have some fun! You will have to build it eventually but a friend of mine done that for maybe a year and a half and the trans was still holding strong when he had it built. O and he ran the max effort tune a few times. Truck had 300K miles on it
I'm with Mike on this one, dropping the trans to do a RatioTek on a bone stock trans is not a great use of time and money just to gain a little more time. If the trans comes out it should be build properly and not bandaided. It is more money for sure but I like to "buy once cry once" and not worry about things again.
To the OP, a TransgoJr on a 6spd does help. Use Mike's springs as opposed to the Transgo supplied trim springs.