Hi guys,
I am looking at replacing the engine in my 99 Gu wagon, it currently has a 4.5 petrol in it but the motor is on its way out.
It is set up for dual fuel and i mostly run it on gas but the fuel consumption is still rediculously high.
On gas i use around 23lt per 100 kms
On Petrol i use around 30lt per 100 kms

It is my work and play car which i drive every day and tow a work trailer which loaded weighs around 800-900 kgs.

On the weekends i either tow a boat weighing around 1.5 tonnes or a caravan that weighs around 3 tonnes, towing either one i go backwards on any incline.
I dont want to sell the car and buy another one because i have it set up just how i want it.

I am not sure whether to replace the engine wth a rebuilt 4.5 or to put an ls1 into it, i know the ls1 conversion will cost another 5k minimum on top of the price of a 4.5ltr but the fuel consumption will make up that cost in 6 months.

I wanted to get some opinions on what would be the best motor of the 2 for towing and for fuel consumption.

Thanks