1995 gmc suburban, farts,pops uphill; changed gas filter and sensors, tuneup etc. what can I do?

when i step on the gas, you can heard the poping sound, like farting, or like does have not enough gas or something. GMC dealer refused to clean injectors.the excuse was "we don't have the adpter for the make and model you own." they inspected the truck and sent me on my way. help