1999 Chevy engine swap, gauges don't work

I have a 1999 Chevy Silverado Ext. Cab Z71 with a 4.8L engine that has 250,000 miles.  I have been considering putting a 1999 5.3L engine in its place but I have no idea of what I am facing or even if this is possible.  The truck is pretty much factory engine wise except for a few bolt-on ugrades with a computer programmer.  I can really use some advice if you have any.  Thanks.

Mike  

Hi Mike, as far as I know, most of the Gen 3 and 4 small blocks are relatively interchangeable. Probably the biggest thing you've got to keep an eye out for is whether or not your truck was originally equipped with a cable throttle or electronic throttle. To keep the install straightforward, I'd try to stick with an engine with the same throttle setup. I know some of the 5.3s are cable, and some are electronic, even within the same model year. Having said that, it's possible to swap an electronic-throttle engine into a cable-throttle truck, but it will require a few more components and changes to make it work. Should be relatively easy. Dimensionally, I think the 4.8 and 5.3 are practically the same. One final note...when swapping late-model motors, try to get the ECU along with the new engine. That will simplify things greatly. Without it, you'll either have to re-flash the old one to get it to work with the new engine, or trade it for another that will work with the new engine. Hope this helps.  

hey...you seem to know a lot of information that i'm in need of as well. my 4.8L has been to hell and back and i'm ready to swap engines to a 6.0L LS2. a few mechanics i have talked to have told me the same thing...all i need is the engine. is this true? i know the major replacements/adjustments would have to be the computer. but would there be any other obstacles that i'll run into???
.CaptnNick.  

....oh and my truck is a 2001 Sierra Ext. Cab, 2WD.
.CaptnNick.  

LS2 is slightly different than the other truck motors. Should be a relatively straightforward swap, but I do know the manifolds on the higher-performance versions (like the LS2) are a little different. Also, not 100 percent sure on if the bellhousing pattern is the same between an LS2 and the other Gen III and IV engines. Regardless, there are adapter plates you can buy to make them mate up. Good luck, and let us know how it goes!  

I am not sure I am doing this right but here is what I have got. I have done a total engine swap for a 1999 Chevy 6 cyl to a 2005 GTO LS2. I got the engine running. I even used to trany from the GTO. My problem is I cannot get the wiring resolved. I live in Shreveport, LA. I need either the instructions to fix my problem or a wire guy in the area to do it for me. I used a painless wiring harness but still have multiple wiring issues. Can you guide me???  

What are specifically having issues with? The gauges?  

Sorry been outta touch. I cannot get the tac and speedometer to work. I cannot find anyone in Shreveport/Bossier Louisiana who can do custom wiring. The computer will not read the rear end.  

Yep...tach and speedo signals are probably the biggest headache with swaps like this. I know a buddy of mine re-geared his truck and put different tires on it, and he had to replace the tone ring on the transmission (automatic) to get the correct speedo signal. That was on a Ford, so I don't know how it works on a GM.

I've seen a lot of guys take out the OEM gauges and get a custom gauge cluster made with aftermarket gauges (AutoMeter, Dakota Digital, etc.) that they can get to work. Sometimes, that's the easiest way to go.

My guess is the newer-gen engine/trans computer is sending a different type of signal than the speedo and tach recognize. I don't know if it's a matter of just re-flashing the computer, or if you could add an in-line modulator that would convert the signal to one that the gauge cluster would recognize. If anyone has any tips or experience they can share, please post!