is 27 spline 8.25 really that weak

how weak is a 27 spline compared to a 29 spline
I have a 99 with a 29 spline but I wanna upgrade to 3.55's from my 3.07's
and the cheapest way to do that is to buy a complete diff from the local u-pull-it for 60 bux
96 and olders are ALOT more prominent in the yard which means I have alot more vehicles to choose from if I go with a 27 spline

my jeep will be more a daily driver than anything but with a little weekend wheeling here and there
but even in stock form the 3.07's just seem weak to me
I plan on upgrading tires but probably only to 30x9.50's
maybe at the absolute max I might go with 31's
ohh and I DO PLAN ON LOCKING IT

is it really that much of a step backwards going from 29 to 27 spline
the way I see it is alot of you guys wheel the crap outta 27 spline XJ's with 31 and even bigger so why is it really a step back on a jeep thats mostly a DD
and I dont plan on getting rid of the 29 spline so if I ever decide to go bigger I will still have the 29 spline laying around for upgrade purposes

Look for axles from a 4cyl, many of them have 4.10 stock. You will love the new power and it will leave you with more options if you decide to go any bigger than 31's.

mpg would suffer too much for me staying with a 30" tire and goin with 4.10s

I am very sure I would love the added grunt of the 4.10s
I am a torque fool and 4.0s would satsify that desire
but my wallet would get sucked dry and I'd never be able to afford bigger tires cause I'd be buying gas all the time
my around town mpg (majority of my driving now) would go from around 16-18 down to probably 14 or so maybe worse

the 27-spline is plenty strong... certainly weaker than the 29 but not as weak as the 27-spline D35 as people tend to assume..

i got a 27-spline 8.25 a few years ago with a Detroit, 4.56s and stock shafts.. it had been run very hard for a year on 33s, i ran it for a year on 33s as well, sold it to a friend who ran it with 35s and replaced thge axles with Yukon as a precaution and went to 37s for a while, he sold it to a guy running 35s as well and its still going strong. all these rigs were AW4s.

if you dont plan to go bigger than 31s you likely wont be as hard on the axle as my experience has been so you likely will have a hassle free experience. i'll never say "never" but i have alot of confidence in the 8.25 axles..

yea I kinda figured it would be up to the duty with no worries but wanted to ask first just because some people no matter what the situation will ask WHY are you taking a step backwards!!!!?????

is there nay difference in u-joints between years
I thought I remember reading somehwre that the 99 was the agood year because it used the big u-joints or something like that
or is that specifically talkin about front axle shaft joints
if its talkin about driveshaft joints what will I need to do to make it work
will I need an adapter style joint for the different sizes of yokes
sorry for the newb-ness here and thanks for the advice

rear d/shaft joints are all the same... the only concern about rear axle swaps with XJ rear axles is rear d/shaft lengths.. D35, D44 and 8.25 have different pinion lengths.. D35 is a shorter axle needing a longer d/shafts.. D4 and 8.25 are basically the same..

ok so a 8.25 27 spl and 8.25 29 spl will be no issues at all to swap
thanks alot