I have a 1995 Chev 2500 6.5 TD. I use it to pull a 5th wheel. When pulling in third the truck is running around 2900-3000 RPM. Can any modifications be made to allow towing in 4th. If trans temp stays down is it ok to pill in 4th. OH, it is a four speed automatic, 4wd.

Towing in 4th isn't really good for the trans. You could install a Gear Vendors (http://www.gearvendors.com)over/underdrive unit.

4th gear uses a sprag that is a bit weak, especially with the pulses that a diesel puts out. When they go, they tend to break up and ruin the overdrive assy. I doubt you would see any mileage improvement in OD pulling the trailer. The main concern is to be sure that the converter is locked up at heavy throttle. If not, it hurts mileage and really cooks the fluid. I put a toggle switch on my '91 to manually lock the converter at heavy loads, because the computer unlocks it above a light load level.

Not to disagree with techs here; I as well as many tow in OD on my 6.5 & have had no problems; what kind of load we talking about, go to the 6.5 forum FAQs look up your RPO codes to see which trans you have I suspect 4L60, if towing often I highly recommend deep trans pan and auxiliary cooler in addition to the factory one.

Extra fluid will help keep trans cool heat is real killer of the trans, I also had HD clutch pack installed in mine but I heavy tow on occasion as much as 18K loaded trailer.

I guess I was assuming that the truck was 8600 GVW, and had the 4L80. An easier way to know which trans than looking at the RPO is does it have 6 or 8 lug wheels? If 6, it is light duty 2500 (7500# GVW) and will have 4L60. If it is the 4L60, I definitely don't recommend towing in OD. If 8 lug, it will have 4L80.

Possibly but GM plays some tricks on you; IMO best to look at RPO codes, just counting lugs still no guarantee some 2500 LD trucks out there I once thought only 1500s were LD. My tranny builder says my 4L80 is plenty up to the task to tow in OD so long as I stay on top of filt changes and keep tranny cool.

8600 lbs GVW will be the 4l80

Look for the MT1 option in the glove box..

Thnaks Guys, I guess I failed to mention the weight of the trailer, All loaded the absolute mas would be 7800 - 8000 lbs.