Don't know which modules you have, but here's a copy of a post I made on the First Great Expedition forum about my Hauler with 27.5 light years jump range. Hopefully by comparing which modules you use and I use you might find out what's wrong.
"I recently built myself the ship of my dreams: Meet the Wallflower, a Hauler specially equipped for exploration. The Hauler can do jumps up to 27.54 light years and has a very fast fuel scoop.
As per usual most modules were selected as D-class modules due to their low weight.
Modules:
External:
Nothing. No weapons, nothing mounted on hardpoint or utility mounts.
Internal:
Lightweight alloys (0 credits)
Power plant D2 (5934 credits)
Thrusters D2 (5934 credits)
Frame Shift Drive A2 (160224 credits)
Life Support D1 (1293 credits)
Power Distributor D1 (1293 credits)
Sensors D1 (1293 credits)
Fuel Tank C2 (included so 0 credits) [see *1 below]
Fuel Scoop A3 (902954 credits) [see *2 below]
Detailed Surface Scanner (250000 credits) [see *3 below]
Shield Generator D2 (5934 credits)
Advanced Discovery Scanner (1545000 credits)
The total costs are therefore 2,932,579 credits including 52720 credits for the base ship. You may think this is overkill for a Hauler but I love this ship so it deserves it.
Comments:
*1: I am tempted to try a C1 fuel tank instead. This will increase the jump range to 29.64 lightyears. The ship could do 2 maximum range jumps or 5-10 medium range jumps before needing refuelling. It's a trade-off and I'm not entirely sure, but I might try it at some point.
*2: I like to spend as little time as possible near a sun, both to avoid intercepts but also because a huge atomic furnace just outside my driver's windshield is a bit unnerving to poor old me. Obviously this module is where a lot of cost-cutting could be made if you're not as afraid of suns as I am ;-)
*3: In my Hauler the surface scanner is mounted in a class 3 module slot, which is a bit of a waste. But I didn't see anything else that I'd like to have in the slot instead. You could put class 3 shields there instead if you want additional protection - no idea how much that affects jump range.
Pros:
Very capable machine for long jumps
Huge cash income due to having a surface scanner and an advanced discovery scanner.
The Hauler is cute as hell and the engine sound is awesome. IMHO only the Asp comes close in this department.
Cons:
One-trick pony. Most notably, my Hauler cannot actually haul anything as it doesn't have any cargo holds left. Also it is completely unarmed so brave-sir-robining is the only option.
Verdict:
I love it. For what I intend it to do it is the perfect machine. Perfect for pilots who aren't looking for a fight. Certainly a keeper for me."