1998 CHEVY SILVERADO

TRUCK HAS 83000 RUNS GREAT UNTIL I PULL TRAILER OR DRIVE LOTS OF HILLS. AT FIRST IT WONT PULL WHEN U KICK IT INTO PASSING GEAR ,TRANS WISE ITS KICKING DOWN SEEMS LIKE IT CHOKES OUT WITH TO MUCH AIR TODAY WITH TRALER IT GOT WORSE AND WOULDNT GO IF I GAVE IT ANY GAS. ONCE I TOOK MY FOOT OOF THE GAS IT GOES,HIT THE GAS AND IT BOGS OUT AND SPUTERS. TURN IT OFF FOR 1MIN AND TRY IT AGAIN IT TAKES MORE GAS BUT STILL NOT RIGHT. SHUT IT OFF FOR 1HR AND RUNS GREAT AGAIN ITS DONE THIS 4 TIMES NOW IT'LL RUN GREAT FOR MONTHS TILL DRIVE UP LOTS OF HILLS OR PULL TRAILER I THINK SOMTHING IS BREAKING DOWN IN IGN.NOT SURE DONT WANT TO WAST MONEY. 5.0 CENTRAL SFI ,AUTO ANY THOUGHTS? CHECK ENGINE LIGHT SAID NUMBER 4 MISEFIRE,LOW VOLTS ON R/LEFT PRE CONVERTOR O2 SENSOR . LIKE I SAID IT RUNS GOOD FOR NOW , CLEARED CODES WITH SCANER NO MORE CODES YET TILL I ASK WHAT SEEMS TO BE TOO MUCH OUT OF IT ?  

First off, the 305 is being worked pretty good in your truck towing that trailer.

Setting that aside, it sounds like the fuel pump is overheating and vapor locking. Anytime there's combustion issues like not enough fuel or timing, it'll trip O2 sensor warnings.

A cam swap will really help your towing.  

This is a suggestion take your scanner with you the next time you pull the trailer when it starts doing this  pull over don't let it cool off and hook up the scanner go to sensor outputs and go to tps sensor. it should read .05 with your foot off the gas peddle and 5.0 at full throttle but when you check it move the gas peddle very slowly and make sure the sweep between .05 and 5.0 there is no break in the numbers, if it goes blank between .05 and 5.0 the tps sensor is bad. A lot of times it wont set a code and it wont show up until it is hot.

p.s I hope this helps you.

thanks
Lee