I didn't think the pieces you need to support stage 4 are available. Most of the 4.6 pieces are no longer available either. But to answer your question. Dinan mods are always expensive due to their supplemental warranty, research, testing etc. And is not unusual they can price where they want as the only source-- as was the case with my 4.6 in 2002.

For your application I would start by increasing the flow of air into the engine and lowering the outgoing exhaust restriction and lowering the effective diff ratios if practical. I think those are the biggest and safest bang for the buck. You can do that without Dinan. If Dinan has the transmission software that is worth the price. I think there are other tunes available but I have no experience as to the benefits but a tune would get more out of the air in/exhaust out improvements because they advance the timing curve some. I wouldn't go to the larger Dinan throttle body because you won't have the larger MAF to go with it. You could replace the clutch fan with an electric one, that get some HP/TQ back. There isn't a whole lot out there but it all adds up. The best improvement for dollar spent is nitrous but it also comes with greater risks. Meth injection will make a shot of nitrous safer but it is not for the faint hearted or someone that does not have the knowledge to work with it and able to identify the symptoms of a potential problem before it happens. I think a 50 shot nitrous and low restriction exhaust only would be a great way to go but you won't find many that agree with me.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas