RPO codes question

[Killain]

I have a 1990 2x4 Silverado that I'm close to finishing restoration, and it looks great. I'm trying find out the factory codes for the rear axel, I have all the codes in the glove box, but two things kinda throw me for a curve. My truck has a code 'GMC & GU6 the latter being a ratio of 3:42. Now the truck had/has a heavy duty towing hitch, but my RPO codes don't show a towing package (I can only asume it was a dealer installed item, but you would think this setup would also have a Posi-Traction rear end, but I can't find any mention of it.

Finally what should I look for in buying a rebuilt Posi rear end ? There are a lot out there, 28 spilne 30 spline and so on. The truch TBI and I bought a "Throttle Body Spacer to go under the injector throttle body. What do you think about the spaces? They clain to ad 25 horse power and 30 LBS touque, which I would love to have a little better off idle pickup. And do you folk think that besides the frame installed towing hitch, ( it is mounted with 6 x 3/8 inch bolts, three on each side / Thank you !

[Six_Shooter]

Towing package does not automatically mean posi.

It sounds like you have a 3.42 open diff, if there sno mention of posi, and hasn't been swapped in at a later date.

[EagleMark]

Nice looking truck!

RPO code GMC is the plant it was made at "GMC : PLANT CODE PONTIAC, MI, USA"

I have a 90 Suburban (old square body still) with factory tow package, it comes with 3:73 gears, oil cooler and trans cooler along with four core radiator. But even back then I don't think the hitch was included?

For a posi if you really need one get it for the splines on your axle, 28, 30 etc...

I've only ever seen one dyno test on TBI spacer and it showed no gains? Although years ago the CFM tech spacer did show small gains in a stock motor, it is the one that opens both bores.

[Killain]

I a sucker for any item that claims to give you small gains in torque !

[1project2many]

Leaf blower!!!
http://www.youtube.com/watch?v=UQ7YWT6rX0o

You can find substantial gains using the stock manifold by cutting the divider down about 1.25" to 1.5". You'll have to weld the coolant and EGR passages that are opened up during that operation but the difference is very noticeable.

You might be able to get a nice listing of what's in your truck using compnine.com. I found a detailed listing for my '99 Suburban using the free pages.

[Killain]

Thank you ! That worked out nicely ! Much better than a carfax in many ways !

[Killain]

Thank you. Do you think "Throttle Body Spacers" are worthless ? I respect your opinion, but so many folks have bought them and are using them, without any mention of the thing being a waste ? They are simple enough so I would assume your right, ( If GM thought for a minute a spacer would increase HP and toque, they'd made the manifold taller. Having said that, I am astounded that the have such a fan base. I have a C5 Corvette and belong to a club and the members there swear by them. I often wonder if they are the 'Sugar Pill' as they all speak of such and such increased performance. Me, I put a K&N filter in mine and it doesn't do much other than giving me the sense the filter is working much much better.

Did your 99 Suburban come from the factory with the "Tow Package" ? Mine look exactly as it douse in the 1990 sale brochure, so I'm wondering it was installed back at the dealership as the wiring loom & bumper mounted pig tale outlet works perfect and the truck is a PA Class II towing hitch, so I can pull 8.900 Lbs. When I redid the restoration we had to remove the weight class sticker and sent me a new one. It has to be right of the state inspection stickers, but not too close so the inspection stickers have to be changed every year and the weight class sticker stays on forever. In the pics below you can see the two inch square receiver where the ball and hitch ( I bought a 2 inch hitch with a 2inch drop as the was the size of the frame mounted hitch.) and the sealed wiring outlet works perfect, lights and electric brakes , Etc. Thank you for your kind assetment of my 22 year old pickup. My grand father always said "If it's worth keeping, it's worth taking care of!"