It sounds like the 2.7L you mentioned has a stock cam.
The modified cam is key for climbing grades, an engine needs to breathe under load and the stock cam cannot do that at higher rpm's.
I would also do a compression check on that engine as it should be above 150-160PSI.
Basically the more torque generated, the better an engine performs on hilly terrain.
On the subject of RPM limitations, Redline between a stock engine and a modified engine changes due to the type of piston material used and carb settings.
The stock cast aluminum pistons will eventually fail above 4500rpm for extended driving due to material heat transfer(melting). A forged Piston is lighter and can take more heat, moving actual redline into the 5500+ range, but at that point you are at the limit of the connecting rods and float bowl capacities(read running lean ).
My mods put the engine safely at 110-125HP, a noticeable improvement and within the max engine output for the drivetrain.
Bottom line, if you need more power and the engine is tired, it is only a few more $ to upgrade.
This week I shipped out a set of my 2.6+L pistons and high torque cam to a list member up north.
I am sure he will post results after his truck is back on the road
