[Mertz]

I am working on increasing the towing power of my 72 Chevy pickup. I installed new plugs and upped the timing so I am at 36 total. I run my test drive up a 1.5 mile steep grade and it will stay in second until about 55 then when in drive it will barely increase it speed and by the top of the hill I am only doing a little over 60. The temp is ok on the climb but when I get to the top and on the level it goes way up. The truck normally runs cool. At the top of the hill the temp will climb to almost overheated and then it will drop to normal in about 2 miles. Does this sound like the tranny is slipping? The revs going up the hill are at about 3300 in drive. I am in the process of change the trans fluid to synthetic. The fluid I removed (4 quarts) was not clear but not really brown. I will change it again soon with more synthetic.

Acceleration on the flat is great. I can hit 80 very easily. 350 with 350th and 4.10 rear.

[Crosley]

Sounds like you have more problems going on than just the transmittin

[Blazin72]

How much of a load are you trying to pull up the hill with your 350?

[Mertz]

Right now it is only the truck but I am working on increasing the towing power to pull my 6000lb trailer.

[F-BIRD'88]

Check the engine rpm gear ratio math after measuring the loaded radius of the loaded tire. (measure from the ground to the axle center)
Allow 5 to 7% for the converter while under load. (going up a hill).