I recently purchased a used 2003 1/2 ton ext cab 4x4 with the 4.8 and 4 spd automatic transmission. It has just over 160,000 km on it and I have all of the service records - it was maintained well.
If the truck is sitting for a while, and it is a little cooler outside (well above freezing) it has trouble starting. It is almost like the battery is very low and doesn't have enough juice. One time (when it was right around freezing) it would barely turn over for ~2 seconds and that was it. I tried twice and then stopped, thinking I will need a jump. After 1 minute I tried one more time and it started.
When it does start like this it makes an odd sound - like an exhaust leak. The sound goes away once the engine is completely warmed up. While it is making this sound the oil pressure fluctuates between 150 and 275. Once the noise goes away, the pressure settles at just under 275.
It seems to shift a bit early under full throttle - in 1st and 2nd gear at just under 5000rpm, and it won't kick down under full throttle above ~110-120km/h.
And lastly, the fuel economy is quite poor - about 15l/100km at a steady 100-110km/h. Both of my other 4.8 powered trucks were using 12-13l/100km in similar driving situations.
Any of you have any ideas?