Truck Repair: concerns on my 94 F- 150 Ford, axle assembly, clunk

Question
Any advice would be appreciated.. The transmission was replaced a few months ago, in hopes of fixing the "problem"
My 1994 F-150 Ford at times will ram up the rpm and clunk into the next gear when I picking up speed to drive.
Today I noticed leaking in the front differential...

Answer
Check the fluid level in the transmission. It could be low, and sucking air.

The leaking front diff....if it has the twin "I"beam type, and is leaking out where the diff bolts into the stamped axle housing, I would try to snug the bolts up first.
To replace the gasket that goes there requires complete, and I mean complete disassembly of the front axle assembly.
Both spindles need removed, and both axles need removed before you can get the differential out of the housing.

Van