Problems starts here. D150 318 bored out on a 727 tf. Trucks has original slant six rear end installed.
In park I have around 1100 rpm idle. Moving to drive the truck idles at 750. Back into park it's like driving it up a speed pump. Truck torques forward and I have 1100 rpms again. Driving through the gears automatically the truck sometimes finds or misses 3rd gear and shifts hard through 2.
The trucks also sounds like its cranking high rpms and working but it's moving much slower than I thought it would before the project began. Ie 2750 rpm and 40 mph in 3rd gear. Just doesn't sound right.

 

Being a truck it has an 8 3/4 or, 8 1/4 both will be fine with the 318.. I would check to find out what gears are in the rear.
The trans could be slipping ? Check the fluid level, shift linkage, kick down linkage Band adjustment anything more and the trans will need further checking

 

sounds like a possilbe torque converter issue odk though i tend to stay away from auto

 

depends what year t could be a converter problem if it is a lock up

 

The engine and tranmission is from a 1970 charger.

 

But what is the rear ?? NEED to find the gear ratio could be 4.56 in truck ???

 

Sounds like the throttle valve on the transmission is stuck in the wide open state causing the hard shifts and not up shifting to 3rd... Bill

 

Actually TVlynn I have a 7 1/4. Starting to think I don't have the appropriate rear end.

 

Is this my problem?

 

Never seen a 7 1/4 in a truck ! it will work.. The gear ratio is what make the difference in speed/ RPM

 

So I did a gear ratio check. wheel turned once and shaft turned 1.75 turns. With that info and a 27 inch wheel base. At 2700 rpm i should be hitting 125 mph and have shitting acceleration. Why is this happening? torque converter? its a new rebuild. Could it be a mixture and timing problem? what should i check next?

 

sorry. didn't multiply it twice for the fact that one tire is braced. its actually a 3.55 gear ratio.